Hedge fund manager Paul Singer helped raise $1 million for Sen. Marco Rubio's campaign Wednesday and is recruiting donors for a pro-Rubio super PAC. (Moritz Hager/World Economic Forum)

This post has been updated.

On Tuesday afternoon, hedge fund manager Paul Singer was ensconced in a suite at the lavish Palazzo hotel in Las Vegas with the strategists running a super PAC supporting Republican presidential candidate Marco Rubio, helping to lead a briefing about the group’s plans for a small gathering of donors he had helped recruit.

The following evening, the billionaire was introducing the senator from Florida to 400 supporters packed into a Marriott ballroom in midtown Manhattan  – a fundraiser that brought in more than $1 million for Rubio’s official campaign, one of its biggest events to date.

The back-to-back events spotlight how Singer has already emerged as one of Rubio’s premiere financial backers, just six weeks after endorsing him. By applying his hard-charging approach to the pursuit of contributions for both Rubio’s official campaign and his allied super PAC, Singer is demonstrating why mega-donors are more valuable to candidates than ever.

While campaigns are not allowed to share their advertising strategy with independent groups such as super PACs, the Federal Election Commission has opened the door to collaboration on the fundraising side by giving candidates permission to appear as guests at super PAC events. That leeway has been seized upon this cycle -- both by presidential contenders such as former Florida governor Jeb Bush, who helped his allied super PAC raise more than $100 million, and by wealthy donors who are helping bring in money on both sides of wall. The top donor to a super PAC backing former governor Rick Perry’s short-lived presidential bid was Dallas billionaire Kelcy Warren, who also served as finance chairman of Perry's campaign.

[It’s bold, but legal: How campaigns and their super PAC backers work together]

Brett Kappel, a Washington campaign finance attorney, said the practice is risky, as fundraisers have to make sure they are not conveying strategic information from the campaign to the super PAC.

“It would be unusual for the fundraiser to have no knowledge whatsoever of the strategic decisions made by the committee, but it’s possible if someone has segregated themselves,” said Kappel, who represents both Democrats and Republicans. “There is a legal way to do it.”

The meeting in Vegas that Singer attended was run by Warren Tompkins and Jon Lerner, two strategists for the pro-Rubio Conservative Solutions PAC. The discussion focused on the outlook of the race and the super PAC’s plans, according to people familiar with the session. Singer, who helped convene the gathering and invited fellow mega-donors to attend, also spoke and emphasized the importance of the group’s role.

Attending such a briefing as a campaign donor is permissible, since the narrowly drawn coordination rules only bans a campaign from sharing its media plan with an outside ally – not the other way around.

Singer has taken additional measures to ensure that he does not convey any super PAC strategy to the campaign by steering clear of Rubio's political operation, associates said. Since endorsing Rubio, he has had no conversations with the senator’s strategists and is focused solely on fundraising on the campaign side.

"Paul, with the advice of counsel, has of course taken steps to ensure that he complies with the coordination rules," said Singer spokesman Michael O'Looney in a statement.

Singer is worth an estimated $2.1 billion, according to Forbes. He made much of his fortune through the hedge fund he founded, Elliott Management, which specializes in buying stakes in companies as an activist investor and investing in distressed debt.

He is among a group of former top fundraisers for 2012 GOP presidential nominee Mitt Romney who have signed up to help Rubio, including Michigan businessman John Rakolta Jr. and Frank VanderSloot, chief executive of an Idaho nutritional-supplement company.

[Marco Rubio wants to unite later by staying vague now]

Singer and VanderSloot were among the co-hosts of the Rubio campaign fundraiser in Manhattan Wednesday. Singer introduced the senator by noting that he supported him when Rubio went up against then-Gov. Charlie Crist for Senate in 2010, despite pressure from the national GOP establishment not to do so.

"I recall getting calls from numerous national Republican leaders telling me that Marco should wait his turn," Singer told the crowd, according to a person familiar with his remarks. "But I was proud to support him then, and our party and country are much better off because of his guts to get in, to stay in, and to win. And I am proud to support him today."

Rubio supporters are hopeful that the heavyweight players such as Singer will help the campaign post a significantly better fundraising haul at the end of this quarter compared to the last, when it raised just $5.7 million.

There are already signs that the donations to Conservative Solutions PAC have picked up since the first half of the year, when it reported bringing in $16 million. When the super PAC went up on the airwaves with its first TV ad on Dec. 1, Tompkins said in a statement that because of the group's fundraising success, it would be able to stay on television continuously through "the end of the GOP primary process.”