If you are really worried-

maxpedition tactical gear retractor through a magpul plate on all mags. Press mag release and magazine zips right to your hip where it dangles until retrieved again. Retractor allows easy detachment. I'm sure it's been done somewhere...

otherwise, drop the mag and maybe live a couple seconds longer because you weren't killed while fumbling with a dump pouch or trying to pocket a mag.

When I shoot idpa I have a dedicated type of pants with pockets conducive to retention and tac reloads. With practice it can be done while only adding 1-2 tenths of a second over emergency/slide lock reload.