Get the BMI flight and donate the remaining 17k to charity (or do AC and donate 5k).

http://www.aeroplan.com/use_your_miles/donate_miles.do

If you're not feeling charitable, do what someone else said and earn an extra 1k for 2 BMI flights. You can buy 1k for $40 or buy $100 of flowers from FTD.

http://www.aeroplan.com/earn_miles/buy_miles.do

http://www.aeroplan.com/earn_miles/o...Partner=FTDCom