If what you are after is the ability to hold the rifle more steady from the offhand position, why not just get a good shooting stick? Then you'd have the stability you're after without the extra weight to carry afield.
After re-reading your first post, I see that reduced recoil was your first concern. I like the idea of adding a screw-in weight (like a bow stabilizer) for the range - or filling the stock with lead shot (if it's plastic), then removing the weight and using a shooting stick for hunting.

IM jaybe