Dollar and similar stores may have instant buttons, sold for attaching another button to accomodate temporary weight gain. I paid $1 for 6.
The design is the same as for removable earings and pins: with a pointed 1/2" (12mm) notched post and spring-loaded clasp that fits over the post and rests securely in the notch. Made to keep a waistband buttoned, they may be stronger than the rigs for apparel pins.
Want to try re-routing your UQ suspension line? Insert a pair of these anywhere through a built up seam, (surrounded by stitches and extra layers) or through already sewn-in zipper backing. Now, direct the line over or under the button.
For longer term, you might not wish to trust the button and clasp. But, this is an easy way to experiment and find the location of a loop or hook you might later attach with needle and thread, ( maybe the bra-hooks HFer John Sawyer recommends). Squeeze the back of the clasp and remove in 5 seconds if you got it wrong at first (second, ....or third time). The point here is to make it easy to find the best routing without becoming attached to the "investment in time" of first efforts.