It would be worth working out who you want to mainly perform for: The radio hosts, or the home listeners. Also whether you will have people call in etc.
Banachek has a CD set out there called Radio Magic that is full of advice on this sort of stuff. I cant review it or fully recommend it as i dont have it...but I trust Banachek's work.
Will you have a chance to do some pre-show beforehand? You can create some truly impossible psychic demonstrations for the home listeners if you do a little pre-show between songs or before you go on (You could use psypher here).
Don't worry about finding the perfect 'trick' - the real secret to mentalism is in the presentation. Even the most basic mentalism effect can be dressed up to look (and sound) impossible.
and wondered if the Magic Café crowd could point me in the right direction.
Better go ask them, then.