Believe it or not, as gorgeous as the music is in “Once” and as much fun as the profane ballads are in “The Book of Mormon,” the casts of both musicals at the Kennedy Center get a little tired of singing the same songs night after night. On Monday evening, however, cast members from both shows will get to go off-script, and for a good cause.

They will be joining Broadway Summer Jam 2015, a concert at Town Danceboutique that benefits rocker Cyndi Lauper’s True Colors Fund, a nonprofit group that helps homeless LGBT youths.

“It’s a very casual evening,” said Jamie McGonnigal, one of the organizers. “What I am hoping to capture is the feeling that you are just sitting in a living room, listening to these actors. They want to let loose a bit and not just sing what’s in the script.”

More than two dozen performers from “Mormon” and “Once” have signed on. They will also welcome Laura Dreyfuss, who is starring opposite Ben Platt in “Dear Evan Hansen” at Arena Stage. (A few other performers from that show are tentatively planning to come, too.) It’s a new sort of event in a city with ample opportunities to hear local performers in cabaret settings but with few concerts that showcase out-of-town talent. McGonnigal speculates that this is just the first of such events he will put together.

McGonnigal, a former actor, organized more than 150 benefit concerts in New York over about 10 years before moving to Washington in 2011 to work in politics, with a focus on LGBT activism. After switching jobs in March — and after the Supreme Court made same-sex marriage the law of the land — he has had a little more time on his hands. He got to talking with his old friend Matt DeAngelis, an ensemble member in the “Once” cast, and decided it was time to organize a concert here.

The touring company of “Once,” performing at the Kennedy Center. Some cast members from that musical and from “The Book of Mormon” will appear in a benefit concert Monday in the District. (Joan Marcus/Joan Marcus)

“I’m back in the game,” McGonnigal said. “What I’ve discovered in D.C. is that the audiences care more about the cause and where the money is going, whereas New York audiences cared more about who the stars were and who was turning out to sing.”

Another difference: lower overhead and ticket prices. McGonnigal didn’t have to rent an empty Broadway house on a Monday night, and Town cut him a deal. “This way, people who may not be able to afford a ‘Once’ or ‘Book of Mormon’ ticket will still have a chance to hear these performers sing,” he said.

Although other local groups host similar gatherings, including the annual Summer Hummer, which is set for Aug. 18 at Signature Theatre and raises money for the Taking Care of Our Own health-care fund, McGonnigal’s hope is not to detract from those events, but to tap into touring casts as an additional talent pool and support good causes in the process.

“The more the merrier. When you live in New York, you live in this bubble, but since I’ve moved to Washington, I’ve seen some of the most incredible theater I’ve ever seen,” McGonnigal said. “It’s D.C. It’s not like there aren’t enough people with money to go around.”

Washington’s siren song

Actors aren’t the only out-of-town talent working in Washington. Often, when creative types discover how good a theater town the capital has become, they keep coming back. That’s exactly how conductor Paul Sportelli found himself commuting between Washington and the tiny tourist town of Niagara-on-the-Lake, Ontario.

If someone had told Sportelli just three years ago that he would be balancing a steady gig in Washington with his job as music director at the Shaw Festival, North America’s premiere repertoire company focusing on late 19th- and early-20th-century classics, he probably wouldn’t have believed it. But then came 2011 and the runaway hit “My Fair Lady” at the Shaw, directed by Arena Stage’s artistic director, Molly Smith. That production broke box-office records and ended up being remounted — with the same creative team but mostly a different cast — at Arena Stage in 2012.

“I hadn’t worked in the U.S. in 17 years,” Sportelli recalled. A teenage classical piano prodigy, Sportelli grew up in Connecticut and moved to Canada in his 20s. Last year, Smith invited him back to conduct “Fiddler on the Roof,” and last week he was in Washington again, this time searching for orphans and runaways to round out the cast of “Oliver,” this year’s holiday musical at Arena. He’s heavily involved with the show, including casting and playing around a bit with the musical arrangements, which may end up giving this production of Lionel Bart’s 1960 West End classic a more contemporary feel.

It is a major departure from working at the Shaw, where Sportelli collaborates with a repertory company of adult actors.

“In a way, the children’s auditions are more interesting,” he said, taking a coffee break on a recent breezy afternoon. “It’s pretty rare to do a show where children are featured so much. The adult auditions were very satisfying. But it was great to have a day when I was just seeing kids.”

That day was in May, when he and Smith stumbled upon a problem endemic to casting adolescent orphans: How can they predict whether a boy’s voice will change between now and opening night in November?

“The challenge with ‘Oliver,’ ” Sportelli said, “is finding enough boys whose voices haven’t changed. You have to use your instincts. You can kind of get a sense of . . . whose voice is right on the verge.”

As a result, the May auditions netted just one Oliver, so he and Smith held an additional round of auditions last week and reopened the call for more ensemble members. (An Arena Stage spokesman said that two young local actors had been cast in the title role and that their names would be announced soon.)

“With a regional production like this, we get to decide — ‘How old or young do we want Oliver to appear? What qualities do we want him to have?’ ” Sportelli said. “We are building from the ground up, and it’s up to us.”

Ritzel is a freelance writer.

Broadway Summer Jam 2015 Monday at 8 p.m. at Town Danceboutique, 2009 Eighth St. NW. Tickets: $20. www.eventbrite.com/e/broadway-summer-jam-2015-tickets-17851639735.