I thought I'd put some pics of the jig I knocked together as all the ideas I've read on here have helped and hopefully someone finds mine useful as well. It's good to have options.
Found a bit of box that would sit over the rear jack arm nicely once the bottom was cut out of it. Welded a couple of mounts on the top. Found some bolt that are a firmish fit through the bikes mount holes and drilled out the mounts with very little clearance. Cut any clearance notches required and welded some 45's underneath so it will self center on the jack. Works great, this is a Supercheap jack that was on special for $125 and is rock solid once it's down on the stops.