Thanks boys. I've read it is not safe, but I wondered if it shouldn't be evaluated on a case by case basis. I was thinking of buying (or making) 10 feet of stove pipe, placing the newer stove on the first floor under the stove on the second floor and run the pipe from the first floor stove into the upper pipe, using the upper stove to create a draft, then starting the lower unit and shutting down the upper unit.
One stove would be directly under the other. I'd run a T to connect them. In case you have any doubts, yes I've been certified completely out of my mind.
I'm looking into making my own stove pipe.