The absolute easiest way to handle this, IMO, without resorting to scripts, is to just pull the beast out of the compendium. Keep the druid character on the board, but off to the side. give the player control over the beast token, and have them use the beast for beast related things (attacks, hp, ac, and so forth), and the druid token for things that don't change (wis/cha.int abiltiy checks, etc.) Keep it simple.