So I've got two seats on the same flight, only because I needed to make a change to my return flight and, because I used a voucher for the initial purchase, it was cheaper to buy a new ticket than to change the old one.

Is it possible to check in and fly both seats, just as a POS would?

Factors: I'm not really a POS--tall but not wide. My ticket was not purchased as such. Names are identical, not MR. EXTRASEAT, as some have suggested here. And my MP# is tied to both.

Also, has anyone yet encountered what happens with UDU under such a circumstance? I ask because I am travelling with a companion that would love to trade with MR. 1015-1k II for his upgraded seat? ( only half joking...i wouldn't have the guts/morals to pull it off even if given the opportunity). Perhaps the check-in system prevents duplicate MP#s from checking in?