I wish i had something better than what i have but it's working for now. My sewing area has a wall of shelving covered by 3 full sized flat sheet curtains. When i need to, i pin a fleece blanket to the curtains and then my blocks can be pinned to the fleece blanket. They don't fly all over because the fleece works just like a flannel design wall does.
I need to come up with a better way to do this eventually but for now it works.