Not precisely what you're asking about, but I've long been known to sew a short 3-inch section of webbing strap to the inside of a winter jacket under either armpit area, giving a stout attach point for a clip-on inside-the-waist holster, only mounted higher than usual. A section of seat belt webbing works pretty good for this.
The idea is not at all new. Texas gunfighter John Wesley Hardin frequently sported a vest with a pair of holsters for his sixguns.