Originally Posted by
n0+4c|u3
That was going to be my suggestion. Or an expanding wall anchor for sheetrock cut to length and a short screw.
Most of these suggestions are overkill!
Once the cables are run and properly adjusted, all that guide needs to do is not slip. The cables will keep it snug to the frame (unless you run them slack and then cross-chain small-small, in which case shame on you twice.) The fastener has only to resist a tiny amount of shear forces. A pop rivet or a small machine screw is all that is needed. You could even use a plastic auto trim anchor that fits the hole.