Your idea of transposing celebrity personalities into the fantasy world is very creative. You can take some elements of their Real Life versions, via portraits and soundsets, and also incorporate or translate elements from the game world, blending to create a playable PC.
I suggest you take sound-samples of the bands... even better, quotes from interviews if you can obtain audio files of radio/tv appearances from the celebs. Follow the guide here to splice your sound samples into a complete BG2 soundset for each character:
http://www.planetbaldursgate.com/bg2...tomize/sounds/