The Dooku I dismantled ran on 3 C cells - 4.5v. From what I understand, the Hasbro boards will take 6v without too much of a problem.
It might just be a case of running power from the battery pack, through the sound board, and then connect the positive bulb wire to the EL unit. This is why you want a board that doesn't have 'flash on clash' effect - which is actually more of a 'blink out on clash' effect!
I've used this to power a large LED (not EL), but the principle is the same.
Somone with more experience wanna chime in?
C.