Eh...just flip it sideways and fire it "gangsta" style...
Detachable mags are ok for pistols and rifles - but for large shotgun shells, I just prefer tube mags.
A semi auto tube-mag fed shotgun will carry just as many shells in the tube, and more in a butt cuff or shell carrier...and fire just as fast. I just can't imagine too many folks grabbing a Saiga and a couple of those big spare mags. It's also easier to top off the tube mags.
Anyways...have fun with it - for the cool factor if nothing else.