I open carry about 90% or better of the time now, but for the 30+ years prior to making that decision, I CC'ed with various types of rigs, the most-used of which was a Crossbreed Super-Tuck. I also have the first prototype for a tuckable IWB rig from Raven Concealment, who was customer-service-oriented enough to help me achieve the same kind of clips on their rig as I was using with the Crossbreed at the time - Velcro clips. They sit behind the belt with heavy-duty Velcro either sewn or glued onto the wearer's belt, so assuming that the belt is the same width as the clips, they are as close to invisible as you can get, which is to say, they are
not totally invisible, but neither are they as obvious as the standard stock clips or other styles that go over the outside of the belt are with most tuckable holster manufactuers.
This is not me or my rig, not even positive whether it's a Crossbreed or not, but a quick search on "iwb holster velcro clips" in Google Images landed me in this gentleman's Photobucket page where he has some pics demonstrating how these types of clips look:
There are variations in design, but here's what a typical set looks like:
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(Note: I don't like that stapled-up construction. Just grabbed a pic from an images search. Crossbreed and others make them with no visible attachment method against the Kydex backing. Mine seem to be epoxied, as they've never given way to sweat or other environmental exposures.)
I bought a Beltman belt with the loop part of the Velcro system sewn into the waistband. Even though I don't conceal much anymore, I still use that belt to carry. They're kinda pricey, but they'll last longer than you will most likely. I've had mine goin' on 10 years now.
Hope that helps.
Blues