What about reserving one week a month to only read books you own? This could work if you only check out library books in big batches - when you return your current batch, make yourself hold off a week before you check out the new one. You should be able to put requested books on "pause," yes?
Good luck with this one. I keep vowing to start checking out one book at a time but I currently have 7 on hand, six on hold and I just read one book I bought.....three years ago? because it's part of the series (Harry Dresden. I'm behind. I want to read the new one - which I'm #14 on hold at the library.....)