The consensus about upgrading TA bookings with points seems to be that it is a no-no, at least until you get to the airport.

You can try through Expedia but I doubt they will be able to help. First, you have to ay to upgrade to a qualifying bucket, I am not sure Expedia can do this.

On the day of the flight, I have heard of VS to accepting money at the ticket desk, then allowing miles upgrades.

Please let us know if you have any success.

Nick