well, maybe he should have LESS dignity. he was supposed to be this big-bad in ROTS, a jedi-killer who would be a real threat to obi-wan later on. yet all that is said of him by the jedi is that he is a coward, and they just send ONE guy to fight him.

giving him a higher raspy voice, and really playing on how greasy he is could strengthen his character alot more. when he suddenly reveals that he can fight later on, it could be a bit of a 'bummer we underestimated him' moment. certain elements would need changing to achieve this, but its worth a thought.

i tried this voice change AGES ago - http://www.youtube.com/watch?v=znm5AllHbG0