You can make a small feeder with sugar water or hummingbird nectar. http://www.formicult...-liquid-feeder/
Ants are quite hardy. With Lasius, as long as they have access to sugary drinks they will be fine for 2 weeks or so. Longer than that and you should have the house sitter chop a meal worm in two and drop it into a bottle cap. When you come back, just toss the bottle cap out. Most insurance companies require that you have someone check on your house daily if you are gone for more than a couple of days in a row (at least in Canada).