Just McGyvered my towel bar, was easier than I feared so thought I'd share my method in case it comes in handy for anyone else.
To replace worn out plastic wall anchors where I had no clearance to use usual metal toggle-style ones (see background below), I used a utility knife to carve a wine bottle cork to make 2 plugs to fill in the holes so I had something firm to hold the screws. So far, works like a charm! Even if I have to replace every 6 months, total elapsed time was less than 10 minutes including clean up (but not including drinking the wine). Incremental cost: zero.
Aside: we have no kids, so didn't have to make this towel bar gymnastics-strength. Not that I myself ever used a towel bar for pull-ups or hanging upside down as a kid, noooo.
Aside: I might have tried the toothpick-and-glue method to fill in the holes, but right now we have no toothpicks on hand. Wine we have.
Background: 2 yrs ago, I carefully laid out towel bars in our low-end (or cost effective, depending on your perspective) renovated bathroom, then completely forgot the layout & instead ended up with the left end of my towel bar at a spot on the wall where there was an HVAC duct behind the drywall (no clearance for regular screws or metal toggle-style wall anchors). McGyver #1 was to trim off plastic wall anchors and use metalwork (short stubby) screws that I had on hand. Held great for 18 months, then got loose.
To fix McGyver #1, I tried to tighten the headless screw that holds the towel bar escutcheon thingy onto the wall bracket, but because the wall bracket was loose there was no way to make it non-wobbly. The wall bracket was loose because the plastic anchors had worn out/had worn down the hole (they always seem to fail in 5 yrs or less, that's why I use metal ones when I have the usual clearance). That brings us to McGyver #2, above.
