Absolutely! Flannel makes a good design wall.
Curtain rods might stand out from the wall a bit, though, which in my opinion, will make it harder to hand press the blocks against the flannel. I like mine against a hard surface....such as like house insulation - foamboard (It's light blue) from Lowe's. These come in 4ft x 8ft. pieces and are very lightweight. I mounted mine horizontally on the wall with lightweight screws. If the wall is a light color -- eggshell/white/buff -- the flannel will likely match it pretty well. I can hardly tell mine is there when there are no scraps or blocks on it.
In your case you might try double stick heavyweight tape and mount directly to the bookcase
Or, having reread your post, you might use ducttape to attach flannel to these foam boards and also to make a hinge of sorts between two panels of them so that you could fold, yet allow them to stand on their own -- like a decorative floor screen would.
Jan in VA
Last edited by Jan in VA; 05-01-2013 at 11:23 AM.