I think your idea will work. Go ahead and buy that tri-fold presentation board!
My design wall is a large piece of flannel (2 yds x WOF). I have a metal closet door in the bedroom, and 3 heavy-duty magnetic clips I bought at Staples on the cheap (watch the clearance bins) that are up at the top edge. The flannel quickly clips up and comes down just as quickly. I can get across the room to see what I want to see. Cotton blocks stay nicely on the flannel. And it was inexpensive.
Good luck and post a pic so we can all see it!