I want to do something similar in my new place. i want to grow japanese morning glories as a living curtain in my living room windows. I am thinking of dropping clear fishing line from a small tension curtain rod for each tendril to climb.You may be able to put a narrow white tension rod near the ceiling and do the same for your porthos. I am not sure how long your wall is.
You could hang something artistic behind it, like a wire sculpture or pretty trellis for the plant to climb. You could also use bamboo to fashion a trellis. You could anchor the bottom in the pot and use either a small nail or 3M clear sticky pads to hold the top part to the wall. you could leave the bamboo natural, stain it, paint it whatever you like.
I am not sure about your climate. if mold is a problem, you may need to clean the wall behind the plant. At some point you will want to paint. I would make it easy to remove to maintain the plant or wall.
