Re: Explain the "tuckable iwb" please...
Gluing a piece of leather to the back of the belt could solve the support issues.
Say your holster uses one clip that is one inch wide.
(1) Glue a 3.5" strap of leather to the back of the belt where you want to holster your pistol. Only the ends of the strap should be glued to the belt. The middle 1.5" should remain unglued.
(2) The unglued center section leaves a channel between the strap and the belt between which the holster clip may be passed.
(3) The holster clip would go over the pants and over the added strap, but between the strap and the belt.
(4) The strap would support the weight of the pistol while the belt itself hides the clip.
(5) Of course, cut the height of the strap to the height of the belt and make it the same color. I'm not a leather worker by any stretch of the imagination, but I have had great results on repairing my wife's purse straps using rubber cement, although there are leather specific adhesives available. (Maybe a cobbler would give you a small amount.)
A cell phone holder attached to the front of a clip will also successfully conceal a clip that goes over the top of the belt.
I used both of these strategies with the holster I described in my post above.