Nothing too unique here - cut the cannon in 2/3 and 1/3 piece, carve down the end of the barrel and drill a hole in his chest and the gun handle.
The remaining gun handle is now a hand-held pistol (which in the photos Warpath is holding back to front... )
It does make him a partsformer, but eh.
The only problem now is he doesn't have a faction symbol, but I'm thinking....