Maybe Gary Lee can rig something up for you?

his stuff is pretty heavy duty..

http://www.telusplanet.net/public/gary2a/rack/vanagonrack.htm

>I tried to figure out a way to attach a moped to the westy but have given up
>on that idea.  So now it's time to hang one mens 27" dirt bike on the westy.
>  Please share what works and sources.  Thanks