Probably a little late for an answer but there are "squirrel proof" feeders available although typically, they're not cheap nor are they absolutely foolproof. Typically, the usual method seems to add self closing "gates" or barriers that flip down over the feeder ports or tray when there is more weight on the perching bar than your average bird or two.

There is also the old remedy of dosing the feed stocks with hot pepper sauce or hot pepper (cayenne, red pepper, habanero powders, etc). Birds apparently have no taste buds that react but the word is that squirrels dislike the hot addition immensely and will leave the seed alone after a few bites. Not saying it works mind you because I've never tried it but there ARE people that swear by the addition.

As we all know though, squirrels have a special little meeting house where all the squirrels in the area meet for coffee every morning and discuss new ways to annoy people that put out birdseed for the feathered creatures. The furry little buggers think these meetings are a secret but anyone who has ever bought even one bag of birdseed knows they exist.