Great question — answering as the UphillTech team:
If you have any kind of drywall skills at all, you could cut out the drywall in the section where you want to put the towel bar, add some blocking (guess you gotta figure out if your studs are metal or wood) where your screws would go, and then repair the drywall. Then you could install your towel bar, screwing into the new blocking.
Full answer by Huesmann: https://diy.stackexchange.com/a/331670 (CC BY-SA 4.0).
Need it done for your business? UphillTech.