Alan Carr, David Walliams, Catherine Tate, James Corden and John Bishop have agreed to perform for one night only as Fake That in aid of Comic Relief.
The sketch will also see the real members of Take That judge the five comedians on their high-energy performance, which will include props, costume changes and tricky choreography.
Walliams, who will be imitating Howard Donald for the first time since his Rock Profile series with Matt Lucas, said that rehearsals for the dance routine were harder than he expected.
"Being in a boyband for the day was really tiring," he confessed. "We had to do all the dance moves, but when Take That did it they were, like, 22 - I'm 39, and I just thought, 'I can't handle this!'"
Bishop, who will perform as Robbie Williams, added: "Obviously it's a good cause, but aside from the charity it was just a great day, I'd have paid to do it."
Other highlights on this year's Red Nose Day broadcast include a special edition of Alan Partridge's Mid-Morning Matters, a music video featuring Susan Boyle and Peter Kay as Geraldine McQueen, and a one-off sketch with Miranda Hart, JLS and Louie Spence.
Comic Relief: Funny For Money airs tonight on BBC One at 7pm.