You could give him a pulse pistol in the other hand.
I gave one of my shas'uis a pistol in each hand with the left hand being made with the fire warrior hand that looks like it's holding shotgun shells. Then, cutting off the back of one of the spare pulse pistols that comes in the pack. I also cut the trigger off the pistol just to get his hand farther in and then I glued it to the hand.
For Aun'shi you probably want to cut off the hand from the fire warrior arm and to replace only his hand with it.
Haven't done it to Aun'shi myself so it's just food for thought.