Thinking about it, there may actually be a way to dump ammo. You'd have to treat ammoboxes as weapons (not sure if possible) and give them a 0 dmg attack that uses a specified amount (50+x%) of its content. If you stop this attack from being listed on your weapons list (not sure if possible) and link it to an ability (not sure... you get it), you'd be able to drop ammo below exploding threshold. You might even be able to fire some more rounds after that.
Still, if it really works, it's complicated to do, it's equally non-TT as not dumping ammo and imho the best way to drop ammo is to FIRE IT AT YOUR ENEMIES!