Using dual 120V for 240?

I am curious.. is it possible to gang a pair of 120V variacs to 
control 240? I assume they would be wired in series, with the center
leg shared between, basically, one on each side of the neutral.

Would this work? and if so, what are the gotchas?
[I see lots of monster 120V variacs on E-bay, but no 240, so I am
trying to be inventive here.]

Michael Baumann
Coiler, Homebrewer, Nerd. mycroft-at-access1-dot-net