A one-piece copy of the gorillamaxx design would be good, made from thicker/stiffer material (I'd buy that myself probably). The other option I've seen done a few times is to have two stock mounts, use spacers between them, and mount them one on-top the other, like a sandwich when viewed from the side or above (use the plastic gearcover mounting holes to mount the spacers). Then the motor can be flipped to face the opposite way, much like the gorillamaxx design, a bit like this:
