In all honesty im not the best qualified to comment, however i will anyways.
First - take it to another dealership. Circumvent the problem
If you have to go back to the original dealer, prepare yourself because they are right. You changed something with the suspension and bushings are a suspension related item. So under some part of the Magnusson-Moss legislation the dealership has you beat. Sorry to say this but i honestly think that they dont have to do shit.
Im not a lawyer, but i do work at a dealership and i have seen stuff like this before....
Sorry to be the bearer of what i see as bad news for you.