If it's more of a "busy" issue, the first option would be to simply add the holiday to your schedule far enough ahead of time that people who rely on you can plan for your absence. If it's more of a "money" issue, I completely agree with the outsourcing idea.
Either way, the key to making this work is to start by making an appointment with yourself a month or six ahead of time. Treat that holiday as if it were an important project - and it rather is, if you think about it. All work and no play makes a very stressed-out person whose productivity is starting to blow a gasket.
Here's an example. Several of us at PFN have invested some time in finding other freelancers who do professional quality work in our respective fields. Not trying to insert a shameless plug, but this just happens to be what we do. After we get to know each other in the forums and perhaps give out a bit of work to absorb a temporary overflow or just as a trial project to check out the skills, we've made some great connections. That way, when we're in a bind, we know where to find help - and if they can't help, they often know someone who can.
But start with reserving your own time. Put it in your planner, and (pardon my therapist impression) give yourself permission to take a break. You'll wonder why you didn't do it before.