call Air Canada and tell them what you want. Normally they can arrange this. If you go back for "white thing", you can claim part refund. check AC' link inside:
-tczaflw(Safe);
2010-4-30{21}(#5993400@60)
Call the customer service no. directly. I did it last year and got open round trip ticket. No penalty when change return day.
-hellofish(hellofish);
2010-4-30(#5993401@60)