thanks for the everyone's input... mission accomplished.
from the original single-pole circuit supplying the fan and light,
I added the light onto a nearby 3-way circuit with the other lights.
then installed another fan, connected it to the first, and converted
the original circuit to 3-way.
I was trying to avoid ganging another switch for aesthetic reasons,
thus the double 3-way switch question.
out of curiosity, is a double 3-way switch even made?
you'd think it'd be easy enough to make, would need 7 screws