Music aside, I know the following suggestion would involve video editing, which I know isn't your forte, Frink, but if you could make Jango's head slooooowly slide out of his helmet with kind of a "schlucking" sound and fall to the ground in this scene, I think the comedic effect would be well worth the effort:

I think I might have seen this gag on Robot Chicken or Family Guy (or some such similar show), but I can't find it now.

Edit: maybe add the sad trombone sound effect when the head hits the ground.