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I suggest you look at Safariland velcro rigs. They had a trousers belt that half the velcro on it, then a Sam Browne that had the other half. I think, not sure, they also had outer belts that would fit your needs (though they may be too thick). The concept of the belt was that the velcro held the pistol belt in place on the trousers like belt keepers do, so it would work for your needs, I think.

And I may be too old and remembering things wrong or out of date, so don't be surprised if they don't have it anymore.