I just booked a solo reward ticket for my 1 year old, as the rest of us were paid J and we wanted to get him his own seat. Presumably you could do what you're saying... I was going to do that myself, but would have had to put a birthdate of a few years earlier to get it to ticket. I just wound up calling Aeroplan directly since I would have had to make the call to change the birthday anyways, and she was super helpful. Took her a bit of doing to get a solo ticket done for a <2 year old, but it all got sorted and she did our seating for us too.