I used to use a short metal ruler for that exact same purpose. There is always something to slide it behind, like a cable hider (those plastic case that run along the walls used to hide electrical wire), a lamp on the wall, frame etc. I spent several years in India, SE Asia, and China and always found somewhere to place it. I think the advantage of this over the wash is that you don't need to dig a hole on the door frame, wall or whatever, and you might find even more places to put it on. I also used it to attach the line of my mosquito net.