I understand your problem. On breaks from school I always had trouble finding a bit of work because people knew I wouldn't be around at the end of the summer. Living in northern New England this was particularly troublesome because the really busy season doesn't actually start until the leaves change, which usually co-inciedes with the start of the school year.
Here's what I had to do: lie. That straight forward thing doesn't work. People, you see, are fundementally stupid. For pitty's sake, if its June and you need to hire some one, hire a college student. Sure they'll be gone before you're ready for them to leave, but anyone else you hire probably will be too. Turnover is an unstoppable juggernaut, and, in the interim, you get an employee who very likely at least has access to a dependable ride.
I'm not deceptive or macheavellian by nature, but I think you should feel free to stretch the truth. In my experience, if you get a job in an average place washing dishes and aren't a bafoon, you'll be doing prep in a couple of weeks, and pantry within a month or two, and whoever hired you will be so happy you're there then they won't care that you're off to school in two weeks. The exec on the other hand will probably be washing dishes because the crack baby he hired at the same time as you and counted on to be there through snowfall was caught slugging vanilla extract in the locker room in hopes of catching a pre-service buzz.
Anyway, that's my two cents. This is a pretty noble board, though, and I'm sure there's better advice to be had.