You could also mount a small rubber pad on the axle housing itself. Then you wouldn't have to make any extensions or drill the car for a mount with wider hole spacing. A 3/8" or 1/2" block of rubber could be glued in place.

I had an old can of that rubber dip for tool handles and such. It eventually dried out and solidified into a solid rubber mass. That would work for what you want to do. Make a little form and pour that Plasti-dip stuff inside and let it dry. Then glue it to the axle housing.