I was thinking about this problem today.
I just took on a multiple carb v8 street rod project, and amongst the conundrums is getting the four dueces to work with a/c.
After some consideration of the options, I've decided to use a throttle kicker, (solenoid) tied into the a/c clutch.
Anytime the a/c clutch is energised, the primary throttle linkage will get kicked open a schosche by the solenoid, (opening the throttle plates on all four dueces) to compensate for the additional load.
Something like this may work for your application as well. /ubbthreads/images/graemlins/idea.gif
background
They used these kickers back in the day to prevent dieseling high compression carburated motors at shutdown.
They were energised at key on, to open the throttle plates to the base idle setting.
They were then de-energised when the key was turned off, allowing the return spring to fully close the throttle plates when the motor was shutdown.
Without them, the motor would cough, sputter, diesel and run on, (especially the high compression varieties). I guess it was a combination of high compression and hot spots/carbon that provided the ignition source, (for the motor to run on without the ignition system providing any spark,) but, either way, closing the throttle plates all the way at shutdown allieviated the problem.
Just another option... /ubbthreads/images/graemlins/dunno.gif