Curtain rod brackets & a curtain rod may work if a tension rod won't. Not sure if your particle board will hold screws though (may need to put some wood glue in the holes). Maybe try sewing a rod pocket in the top of your fabric and run elastic through it, and around to the back of your bookcase. Trial and error on making it tight enough to hold in place before sewing the ends together. Kinda like they used to put skirts on sinks.