My original design for holding up the front curtain was a vehicle hanger rack that hangs from side to side and I installed command strip hooks on the pillar to hold it, but I quickly learned that it would not work as the material for the curtain would not slide side to side. It was also heavy and when I moved the seat forward and back I would hit it knocking it so the hooks fell off.
For my trip I got rid of that idea and went to a light weight budgie cord that attaches to cubical clips on either side pillar. The cubical clips have two pointed ends that poke through the the headliner without hurting it.
These plastic clips didn't work either as the plastic clip would fall off the metal pins under any stress to the material.
I have two pins and two clips to hold the center of the curtain.
I just pull the material across from behind the driver's side and use the clips and pins in the ceiling to hold the cord/material in place.
This is working much better and there will be no damage to the Prius. I just need to pull out the pins when my trip is over.