I did it this past Saturday. I booked an 8 credit reward flight on the 9pm flight about 1 month out (only BC reward seats available on the 9am), and used a credit to pay for my wife's seat on the 9am. My plan was to pay the $25 same day change fee that morning. Seating chart showed 27 open seats the night before, so I wasn't worried. Woke up on Saturday and saw only 9 empty seats. Headed to the airport and wasn't able to do the $25 same day change (sold to capacity), only 5 seats showing empty, but could pay $514 for a seat. I went with standby, and 20 minutes out there was still 14 people missing, so I was given a seat. Wife and I returned last night on the red eye, I booked an elite exit row and paid $20 for my wife, plane left full.