I haven't gotten an STP yet (keep putting it off), but you're asking for a lot. You want to keep it in place, minimize the bulge, not have the STP against your skin, but be able to "hook it up"--put it against your skin--at will?
I love TranZwear for my packy. One reason I haven't gotten an STP is that I'm not sure how I would wear the thing. I don't see a good way to use the Snuggler or the Floater with an STP, and I don't think the Commando would work. But the Natural might work if you leave the ball portion out of the little pouch--that is, next to your skin. Or maybe you could trim away some of the pouch--but that would leave more of the STP in contact with your skin.
The owner once said he was working on an STP design. I don't know what happened to that--maybe people are just using the Natural.