just got this from Léo at Arturia tech support:
Unfortunately this would not be currently possible,
The sync source is defined by the clock source, which prevents midi start and stop messages to be listened to if the clock source is set to another source.
So for instance say you want to use internal tempo, only the onboard start and stop would work,
So to be able to do this you would need to send both start and stop as well as clock messages from the pedal in question.
If the pedal doesn't provide clock it would not be able to effectively launch the unit.