Not sure if this is correct, but I'll throw this out there in case anyone has a US and JP board to test with. A friend told me that if you put a blue board onto a motherboard (doesn't matter which region motherboard) and set it to freeplay in the menu, it actually unlocks free play for the Japanese board if you put that on next. He says the board stays like that until you put a different game on and he says it works due to how much code both games share.
I presume that if you can unlock freeplay for the Japanese board, that it would get lost like all the other settings if it's powered off for a while.
So what do you think? If it works it would be nice to set our 2X boards into freeplay mode so we aren't digging around inside cabinets to put coins in.