Hi loveslap,
I haven't done exactly what you're suggesting, but I have used different modules into the pedal in of the Tempest to (try to) control various functions with varying results. The pedal ins seem to have limitations that aren't exactly spelled out in the manual. For example, I have tried using audio rate LFO's and for some reason the Tempest was not able to go past a certain frequency-- I guess it maxes out at some point.
I suspect what you are trying to do is possible-- are you not able to test this out yourself? Depending on what you are trying to accomplish, there may be a clever way to take care of it all within the Tempest.
Are you able to share more details about the patch you have in mind? I can try to put it together if you don't have a Tempest (or whatever external gear you have in mind) available.
Regards,
Steven Morris