You could always though a bolt through them. Check out this pic that I drew of what i have used. (apologies for the old sketch, it was before I had a scanner or digital camera.)




its a bit crude, but this way the mount acts the same way as normal, but if it cops some excisive load, it hits the nylock nut and stops the mount from over streching.

It doesent transmit any extra vibration into the chassis, so it feels like normal, but with the insurance of a $5 bolt.