Did you add a picatinny rail to your Bushmaster? If so, you can grab swiwel mounts off ebay or ebairsoft, and attach a 2 point sling, 1 end on the swivel, the other using cord/lace, tying it around one of the pump arm. But imo, slings don't go well with pumps...
I would suggest getting yourself a shotgun scabbard, or building one that suits the Bushmaster in size. They come in MOLLE platforms, so you'll need a vest. Or, you can have the pump with no barrel, and get a large size pistol holster, with the barrel somewhere else.