One of the walls of my cinema room has a rectangular cut-out that's 1.8m long and 2.1m high (approximately 6′×7′). I have a blackout curtain with eyelets that I'd like to hang in this archway so that I can watch TV in the dark. The wall is 110mm (≈4″) thick rendered single-brick. I would prefer an installation within the archway rather than on the wall.
I was initially thinking that I'd use an expanding tension-rod but my mum (who's hemming the curtain) doesn't think that it would support the weight of the curtain. I've also seen adjustable pillar ends which can fit a rod that has been cut to size.
I'm renting so I would prefer something temporary but I can contact the landlord for permission if the best option involves some drilling. What are my options?