Sounds interesting. The guy talking about the "cravat". I can't believe this is ancient knowledge now, but anyways, the old GI med kits came with an OD cloth triangle designed to be used as an arm sling, or to tie a dressing in place. It was commonly used as a "cravat" or neck scarf, similar to what the Boy Scouts (there's another anachronism) used to wear. He's saying you could use it as a diaper wrap around your kit, cut to size, and tied off at the top. Good field expedient, using issue(d) kit.
The inserts will work in this case, but I would think, by the time you do all this, you could have just bought another mag pouch, with a (adjustable) top flap. Or any top flap pouch really, that's the right size. Unless you are stuck with issue kit, the Sgt Maj says you must use, you have other options.