Ore Oduba and Sonali Shah (from Newsround, apparently) have also signed up.
ETA: A full-ish list from the Beeb site.
Ore & Sonali – Newsround
Rosemary Shrager & Kim Woodburn
Shaun Keaveny, Mark Dolan and Hal Cruttenden
Lee Nelson has already done it.
Couldn't they find somebody else?