I agree with what seems to be the consensus: for it really to work the U needs to give out free T-shirts.
IMO, here's what they should do if that is not an option: email everyone who has a ticket on Saturday or Sunday this weekend, maybe a few people will buy the $10 black shirt as a Christmas present. Then follow up with another reminder email on Monday 1/5, the day before the game. Finally, sell the black T-shirts the day of the game in the concourse for $5-10 each and make sure it is clear where the T-shirts are being sold.
Also, for those saying the blackout won't work, it already has worked to a certain degree as the game is essentially sold out. Marketing 1001.