This is probably a terrible idea, but I discovered today that SET FOREIGN_KEY_CHECKS = 0; will let you add/remove data that would normally fail if there was a foreign key constraint that failed. Obviously you could quickly see lots of 500 errors if you're not careful, but in a bind this actually is quite helpful. So use it with caution — if you dare.

And then to reenable foreign key checks, you can just run SET FOREIGN_KEY_CHECKS = 1;