My Bontrager Race-X-Lite is reversable. I still use it that way even though the bike is now no longer the dedicated tri rig. Not sure if it would give you enough though. Have you talked to anyone at Aerus Composites? I think they are still out of Atlanta, GA. I've tried to find an excuse to buy one of these posts:

http://aeruscomp.com/index.php?main_...products_id=12

300mm looks to be the max length they carry in stock, but they may do some custom work. Could be worth a shot, although likely more expensive than having someone weld one for you.