Badmelonfarmer, yeah, that's the problem. I was thinking there may be two ways to address it…
First idea, GCP MIDI Out (PC and CC) to TF MIDI In (receiving both PC and CC set to "tap"), TF MIDI Out (set to Thru) to MF MIDI In (all on same channel, receiving both PC and CC set to "tap"). That wouldn't involve any merge boxes, and although technically MIDI Clock isn't used, setting both pedals to use the same CC for "tap" should sync the tempos as long as the GCP is used to set them. What this won't do is reset the tempo when it's stored as part of a preset.
Second idea uses a merge box to take PC from the CGP and merge it with clock data from the TF.
This would not work, as unfortunately I don't think you can set the IA switches to send CC's on different channels… you can with Program changes, but not CC. I thought about doing that when I was trying to setup the Axe-Fx and TimeFactor….but it is not possible on the GCP…. maybe on other MIDI controllers though….oh and I feel ya re your Eventide addiction! LOL