Why don't you just get a thru-the-glass robe hook? It requires a 1/2" hole in the glass BEFORE it goes to tempering. It looks much less intrusive than an over the top hook.

-Babka

Too late. Glass has already been tempered.

Look at Command Hooks. They are now making brushed nickel or chrome look, etc. in a few different styles. I wouldn't call them top quality, but they are fine looking and will hold a towel easily. You could put one on the wall nearest the entrance so you can reach out and grab your dry towel. Put it above eye level and it won't be noticeable at all. They won't damage the wall or tile/marble. If you have enough room in your shower, you could put one IN the shower out of reach of the spray.

I've had two (to hold wet washcloths to dry before putting in the laundry) in my shower for about 3 years and they seem to do fine in the damp, even direct spray when cleaning the shower.

I always just toss mine over the shower door. Our shower is large enough that the half of the towel that is inside the shower does not get wet while I am showering.

Yes, they make Command Hooks in a couple different profiles specifically meant to be used in wet places, i.e. showers. Cheap in cost, but better looking than the over the top hooks I've seen.

-Babka

Maybe I will be able to use the door handles as a place to hang the towel before stepping into the shower or else if I hang it over the door at the far end of the shower, it won't get wet.
I think a D shaped door handle could probably be used as a makeshift towel holder as long as the opening is big enough to feed the towel through..

Or maybe one of these high end suction hooks?

Here is a link that might be useful: glass door suction hooks

Old thread but reading your question gave me an idea for my similar problem: if the rack is designed for over a bathroom door, maybe it could work for a shower door if some stick on rubber or silicone pads were used to narrow the gap. And I just realized that they could also be used between the shower glass and the other points where the rack touches the glass. You don't want metal tapping on tempered glass.