Magnum Sling Point

Print two with a reasonable infill and/or shells. You could glue, but I just let the blaster hold it together. You take out the wrist rest bit, then slide both pieces in, lining the slot in the back of the sling point with the ridges in the handle scales. I use a key-ring to make it easier to clip to.

EDIT: New version added that doesn't require a key-ring. I recommend printing so that the bit sticking out is solid.