If you set the cradle such that it sits roughly in the middle of the lens shade when the lens is at infinity, it will wander to the back of the lens shade when the lens is extended. It could work, but might scar the lens shade over time.
I'm wondering what the problem is that you are trying to solve. Vibrations?
The 180/2.8 is a bit worse IMHO than the 135/2 ZF.2 in terms of leverage exerted on the mount, but this is not based on measurement but just an impression I got from using both lenses. The ZF.2's main fault is perhaps that the focus ring is easily turned accidentally and the focus creeps when the lens is pointed down. Perhaps a different grease could solve the second problem.