I had a bunch of SW drink coupies with expired dates, so I did a quick search.
It appears for coupons to be eligible for the exchange, they had to be issued with Business Select airfare before Aug. 2010 and have no expiration date on coupon. The exchange form had to be mailed before Sept. 2 of this year. Oh, well...it was hopeful for a moment.
Southwest drink coupon mail-in form
**edited for clarification.