Just for reference, you can drill and tap the body. It's not particularly difficult since the stainless is thin. You then need to use a steel screw and fit it very short (about two threads worth). It's weak relative to the rest of a mag, but not bad if you don't beat on the feed too much.
A hole forward of the feed port is easier to drill and tap, but you really have to be careful of the interference with the barrel. A hole behind the feed port has to consider the body bushing, but the bolt spring doesn't fit so tight like the barrel.