Dave, Gordon had this exact problem with his Jaguar (Jag-ooh-ah). He combed the earth searching for a solution and ordered millions of dollars worth (not too far from the truth) of trial valves seeking a solution. Alas! He he found a valve that was adjustably restricted one way, full flow the other. He even set up a wind tunnel to check the under carriage action using this, wondrous new valve.

All kidding aside, it seemed to be a brilliant solution. I'm sure he'll see this thread and comment. If he doesn't I'll call him and have him get the info to you.