Given the clout of this (or almost any) level 20 in this scenario cutsy ways of creating fraudulent funds would be pretty similar to some billionaire like gates musk or Bezos engaging in credit card fraud for the lir Starbucks breakfast bill just because they understand how it would work... sure they might be completely capable of doing it but actually doing that would be an absurd risk to avoid what is effectively an expense not even rising to the level of an inconsequential trivialityKilling your employer as a mercenary seems like a pretty bad decision. Especially when said employer doesn't need to keep a fortune, since they can make the payment on the spot. And if they break concentration before the first hour after paying you, your fortune goes poof.
On the other hand, you don't think Geased creatures won't want revenge if they manage to get free? Good luck with that. People disappearing seems like a thing that gets adventurers called in. You know, the groups with trackers and spellcasters?