I wouldn't do it... Flex plate can flex, oil may go everywhere causing it to be of balance... Stick a transmission behind it - just make sure it's in nuetral and you run a hose or steel line between the two cooler fittings.
Yes, that is what worries me most that the TC will start to flex and come off from the crank.
I'll modify the teststand so that I can mount the tranny to the engine.