Kate Hudson and Sarah Jessica Parker are set to make appearances in the next series of Glee.
TV executives from the US Fox network revealed that the actresses will join the cast of the all-singing, all-dancing show for limited runs next season.
They said the show, which experienced a fall in ratings across the pond this year, is "poised for a creative renaissance" and will also move to a Thursday night slot.
Meanwhile Fox, which also produces the US version of X Factor, remained tight-lipped over reports that Britney Spears was joining the show as a judge.
Simon Cowell's stateside show did well last autumn but didn't live up to the creator's inflated expectations. Shortly after the season ended, judges Paula Abdul and Nicole Scherzinger and host Steve Jones were dispatched.
"Not to be negative about the people leaving, but we just felt the mix could be more effective and more entertaining," said Peter Rice, entertainment chairman for the Fox Networks Group.
American Idol remains Fox's centrepiece, as it has been for the past decade, but the show lost a startling quarter of its audience this season in the US.
"This year was a bigger drop-off than we anticipated," said Fox Entertainment President Kevin Reilly, who promised changes for next season, but wouldn't be specific.
"There's a lot of life left in it," he added.
Fox also announced two new comedies. Mindy Kaling, author of The Office, has created and stars in The Mindy Project, a romantic comedy about a doctor looking for love. The other new comedy, Ben and Kate, is about a pair of odd couple siblings.