Just lean the boards against the wall as close as possible to straight up so they don't fall over.
Unless I'm not understanding.
Well, DUH!! on me Mark. I misread your reply to the OP, and thought you had misread the OP! ;-(They always fall like a bunch of Dominoes for me leaning against the wall. That's the reason I lean them against the pipe. If there's any tilt, arrange the tilt so it tilts towards the wall.
It's also easier to sort for me with the pipe vs trying to hold a bunch of heavy boards. I just lean them against the neighboring pipe 16" or less away. I'm getting to a point where things in my skeleton have started needing overhauling. Less chances for things to go boom are a good thing.