Jack you are making me drool with envy... 400/2.8 wow. v1 or v2?
Matt - one thing you can try for stability is a shoulder brace. A relatively cheap one from Manfrotto. Though advertised for a monopod, it can be attached directly to the tripod ring or camera. Since it also moves at the hinge you can kneel and put the thing onto your thigh. I have one though it has never been used...
http://www.bhphotovideo.com/c/produc...Brace_for.html