make a batch of boric acid, sugar and water. Not too strong, here's the formula I have.
1 tsp boric acid
6 tbsp sugar
2 cups water
put this mixture in their path. They should swarm it, you don't want them to die on the bait as you want them to carry it home to the nest. It might take a day or so but they should slowly stop coming to the bait. You can put some cotton balls in something small like an old plastic film canister, punch holes in the bottom for the ants to get in and refill it when it gets dry.
Good luck,
