So you have a mag fed gun....you want to put it into a single shot stock...and want it to work like a single shot without using a single shot mag?
You can do it, essentially youll need to make a mini single shot mag to hold the round, and more than likely epoxy it into the stock .....this will require some light metal fab and some inletting into the stock.
I've done this with savage mk2s that I converted to single shot