Easy solution, you transfer from Legacy JP to Legacy NA/EU, your friends transfer from Non-Legacy NA/EU to Legacy NA/EU. Though due to the fact that Legacy servers economies are mature, stable and cheap I can see more people wanting to get on Legacy than get off (why pay 5m for Materia when you only need to pay 500k on Legacy.........) so really, Non-Legacy to Legacy shouldn't be allowed as it gives Non-Legacy an economic advantage.......