You could ask them to make it with mezcal instead? But I suspect in this case they might not, since it's promotional anyway... and yeah, I think you ruin perfectly good booze.

There is a restaurant out here in Leominster called (tellingly enough) Mezcal that has some really good mezcal-based cocktails. We went for a pre-Cinco dinner and had a pitcher of their "smoky margaritas," which are made with mezcal.