Is what you really want a bit that looks like a mechanical arm that could hold the weapon? One that looks sturdy enough to actually accomplish without breaking?
Look at this pic from my gallery. The Dread's claw arm. The piece coming from the shoulder is the leg off some sort of set in place gun emplacement I somehow had in my bitz box. I believe it held a lascannon turret. I just cannot think of the model's name. Defense turrets probably.
(If I'm way off here, sorry to have taken your time)