Eventually someone will hit on a solution. I think the key is to prevent that drivers side arm from twisting, as others have said it's design to fail in the event of a rear impact I believe ( correct me if I'm wrong). The arm if you look at it is a H-beam which is a strong section but if it's twisted it will fail from that notch they have cut.
Only other option is to reinforce the arm.
Ugly as it is, if/when mine fails I'll be interested to see how.
These are volvo engine mounts one top and one bottom with big end bolts going through the centre to 10mm thick steel sections one on the left and one to the right. If the nose lifts enough it will then stop after 10mm (I'm guessing), which I think the rear diff mounts can accommodate, and fingers crossed that's not enough to cause a failure. Problem is will it then try to pull the rear of the diff downwards around the new centre of rotation as torque is continued to be applied and fail anyway. I think this is the scenario for failures in high powered MX5's
I think Skov is right though if you are solid mounting anywhere then it has to be all round.
Useful link...
http://foxed.ca/rx7manual/2003mazdar...101025T09.html