I was going to recommend eye and hook screws but since you are using glass I would suggest using either closet rod holders or just using wood/branches that are shaped in a way so that you can create elevated perching areas.
For my Chondros I use rod holders...however I feel it takes away the "natural" look so I'll be using eye and hook screws pretty soon.
EDIT: Actually I forgot who it was but someone on this forum uses a ladder for their carpet python. Seems like a pretty good idea as well for a GTP, if placed diagonally to create different levels for thermoregulation.