Didn't say it was impossible, just difficult.
For example, if you had a MIDI merge device (a small box with a few MIDI in and one MIDI out – the ins are merged together carefully, and then fed to the out), you could set the first Factor to MIDI out and all the rest to MIDI thru.
You then feed the first one from the pedalboard and connect its out to the merge unit. You also connect the pedalboard to the merge unit which feeds the other pedals. This will allow you to get MIDIclock from the first Factor and feed it to the others, while also allowing the pedalboard to control everything.
If you are using all these units as described, you probably will want a single tempo source.
