Fake cans to double as barrel extension for Calif. OAL

I've been wondering about making up the 30-inch overall length requirement in Calif. by attaching a 2.5" butt extension and using a fake can to make up the remaining 2.5". The 4.75" butt extension just throws the hold of the gun way off--it no longer makes sense to have a PS90.

Is it possible and advisable to mount a fake can forward, so that it extends past the muzzle of the PS90? I don't mind cleaning the gun and the fake can frequently, so long as I can shoot it in Kalif.

Thanks in advance for any advice!