It shouldn't be THAT hard to find volunteers.
Where I work I know of at least two squadron execs (thats right, EXECS) who volunteered since they live on the patch and are staying around at Chrimbo, so saluting the flag a couple of times and taking some chocolates to the guys and gals on guard isn't too much of a hassle. I didn't see any blunties doing the same though!
In all seriousness, there must be enough people on the patch who stay around to cover the period anyway. As a sweetener they can be given immunity from duties for a while as a reward.
Simple really.
BV