i bought extra hinges during my build for extra stability. just google freezer hinges and there is a site that has all kind of hinges for all kinds of freezers. You could pick out a set that you could convert to a rear mounting hinge.
The problem here lies that when you attach the hinges to another part of the freezer they will need to go into a sturdy piece of the freezer no just the thin metal wall. Also, you will need to make sure you don/t hit any of the important cooling or electrical when you start tapping a place for the new hinges.
SHare a pic with the goup. Someone should be able ot help you out on here. Id say you should stick with the kind of hinges you have and work around it. Also, be flexible during your build. If you have a concrete plan and come across obsticles you'll get pretty flexible. Check out my build.