Brian Kelly wrote:
A pair of caps
mechanically coupled via an insulated shaft coupling but completely
isolated electrically from each other should work.

Yes, that's what I had in mind. Mine are side-by-side with a
non-conducting fiber-chain connecting the shafts. Same with my
two rotary coils. When I said "dual-ganged", I meant mechanically
ganged, not electrically ganged.

| |/
Coax center wire--------|/|--------feedline--------
/| |
ganged variable caps to dipole
| |/
Coax braid--------------|/|--------feedline--------
/| |

And of course, there needs to be a choke between the coax and
the caps.
--
73, Cecil, W5DXP