Is there trim in the crease or it is a sharp corner? If there is trim and its not painted clean over, you can cheat and use paperclips. Fold the long leg out straight, so its horizontal, and the short U curl down at a 90, so it forms a hook. If you stick the horizontal wire in behind the trim itll usually wedge in without damaging the trim or paint visibly and hold enough for a cat5e.
If no trim, the sticky hangars are probably the best. Be careful not to buy cheap ones that might fall down, leave residue, or stick too hard and rip the paint off when you go to remove it.