Marc is absolutely correct. In fact you dont even have to put all three cabins on the AMX Platinum card. As long as the Cardholder is travelling and all the charges are on an AMX card of some kind it works.

I did not realise that the actual cardholder did not have to actually pay for all the cabins until recently. I always knew you could use any AMX card as long as you owned the AMX Platinum card.

You just use the AMX Platinum card to secure what they call a "tracking" number from AMX Platinum and they use the same number for all three cabins.