Sprinkle a little cream of wheat around the mound and they feed it to the queen(s) and they explode (heard this on WBAP back in the 80's).
I heard that the best stuff to use is DIATOMACEOUS EARTH from the pet shop. It's a white powder used in really good Aquarium Filters, especially for salt water setups. It's the skeletons of tiny microorganisms. On the ant's size level, it acts like ground glass...and if they walk over it, it tears them up real bad. Bad enough, they say.
The other thing I'd try is very effective on roaches, anyway. I once mixed some "Confectioners Sugar", powdered sugar, with Boric Acid from the pharmacy. Like Diatomaceaus Earth it is said to be harmless to pets and livestock. It ended the problem dramatically. Quite amazing.
The other thing I heard about for bugs...maybe ants too...is Baking Soda. They say they eat it, then blow up. Go figure.
I think that the Diatoms would perhaps work, and maybe the cockroach-bait sugar and spice.
Then, there's always the Chili Option.