Well we could also go with the basic princess in distress story, if let's say a princess visits the temple after hearing about the MCs feasts and asks him for help, as she is supposed to mary an older and fat guy in grey fort.
You convince Vixxenatrix to attack the caravan at the western crossroad and than "save the princess" from the "monster"... your reward could be the girl, afterall you are already the mayor of Weirdwood and have a pretty good economy (thanks to your drug deals with the Elves), so maybe her financially strained dad would hope to forge an alliance with you.
For Vixxenatirxs reward she could hand the MC a treasure map from her stack and order him to recover it in order to build a nest for the kids.
Adding Tinkerers Humor in it the plan could even fail as the Caravan is being attacked by bandits before Vixxenatrix appears and she than saves the princess by killing the attackers