At the point of departure, all institutions seending any check or electronic fund to Mexico must tax the money.
They could send cash and get around everything.
They could send their endorsed U.S. check to a bank in Mexico. I suppose the gov’t could require U.S. banks to withhold a percentage of all U.S. checks cashed in Mexico to block that.
I don’t know. There may be problems with it. Good thinking though. There may be a way.