Combine equal amounts of canola or olive oil with liquid lecithin (available at any health food store or natural foods co-op). Store in the fridge. It can be stored in a pump bottle to squirt it on. I keep mine in a container and paint it on with a silicone pastry brush. Actually, my little ones love to "paint" the dishes for me.
This is very economical because a little goes a long way. The lecithin lasts forever, and it makes clean-up a breeze!