I didn't realise Hobie did a freestanding rig, thanks for the tip - found it on their site: http://www.hobiecat.com/sailboats/bravo/
It's not the most elegant of solutions!
I thought of a hollow drop in tube down thru the beam onto a dolphin striker. I ruled it out as I was trying to avoid having a dolphin striker at all. I also thought it would have to be really big to take the fore and aft loads without any additional fore and aft bracing - then the solution is to have a kind of diagonal dolphin striker. But then the design is getting more and complex and the idea of the freestanding mast was simplicity.
So now I am back to square one in my reasoning - a conventional stayed rig might be simpler all round. It may be better to think of rapid rigging systems.