Is Southwest one of the airlines on which you have award tix? Last X-Mas season I used free tickets to fly on WN to Florida from CA and was able to work around the blackout dates allright - my outbound was on 12/20 and the return was 12/27, if I recall correctly. I think these were both Mondays and apparently not in sufficiently high-demand to be put on the blackout list. They seemed to only have about 6 or so dates that couldn't be used, I think the weekend of and the weekend before the holiday (and of course the 25th itself seems to very rarely be a blackout date).
Y.