Yup, far as I know. Thought I once saw some reference to an ambidextrous mag release for another gun, which was based on a multi-piece unit which used some sort of linkage or camming system for the new right-hand protrusion to pull the other side in when depressed.
Sorry I'm not artistic enough to diagram the idea.
Conceivably I think it could be done. I would probably be easier to rig up a backwards unit, put the spring in the other way, and cut a second mag catch notch in the mags. But then you lose mag interchangeability with others and that is not an attractive option.