Some people use a dust cover type mount, but if your current dustcover isn't super tight, it's likely that you'll have some serious POI shift with one of those. However, it's the cheapest way to rear mount a scope for traditional use.
The one I've had the best luck with is made by UTG, and it clamps to the barrel up by the forearm, and gives you a tri-rail setup similair to the Springfield M1A SOCOM.
http://www.amazon.com/Socom-Tactica...=sporting-goods&ie=UTF8&qid=1333244372&sr=1-4 The only problem is that you can only use long eye-relief scopes or other optics, such as holo sights. Say what you like about it, but know that I was able to hold about 1.5" groups while using this rig with a Bushnell TRS25 red dot.
It looks a bit funny, but no permanent modifications have to be made.
Wow, how'd I manage to field TWO optic mount questions for obsolete Russian weapons systems in one night???
