here's what ya do, it dawned on me, that it's not hard, just requires you to tell the player to sit down and stfu.
here goes:
As the player spawns, you give them a pre-designated set of weapons (say, a gun, a crowbar, and anotehr gun, plus a nade, and some explosives, and anotehr gun, just to be sure), you then set up triggers in your map where you want players to have to give up their guns to get, and have that trigger a player_weaponstrip, and spawn that set of weapons right there on teh ground, can't even remember the entity to do that, I'll find out if no-one else steps forward with the answer, though.
and there you go, they won't drop the guns when they get shot (don't think that's what you wanted anyway, right?), but you can force them to drop teh guns, you have to make sure that they get a certain set of weapons though, just so it looks like they've dropped teh guns they had, not just lost their guns, and had some random ones spawn instead.