Kate sounds like a good candidate since she tried it before with Lucas and Sami’s twins. If I remember she talked or blackmailed Nick into falsify the test to EJ was the daddy to both of them. BUT she was never part of this and supposedly nobody but Chloe, Phillip, Nathan, Stephanie and Carly knew about the possibility that Phillip might be the daddy but that’s never stopped the writers before and Kate does know everything that goes on in that town.