Truman,
I think trying to devise a handicap system for different stances is unworkable. Except for those of us physically unable to stand, shooting off-hand is definitely the most demanding and challenging.
However, I wouldn't be adverse to trying different stances - even make up some if we want. For instance, how about a match Sitting Off Hand. This might be fun, and it would allow most if not everyone to participate on level basis. Just a thought....
Personally, I think Standing Off Hand is the most rewarding long term because you'll shoot better in all other positions once you're a consistent Standing Off Hand shooter.
Just my thoughts...
George