I wonder if there is another way to leverage this. If they think they are going to make an absolute killing on the financing, I wonder if you can get them to come way down on price...
So, the approach is: "I don't care about monthly payments or interest rates, I just want the best price possible." Then make it clear (without being obvious) that you are willing to be totally fleeced on the finance side of it so you don't end up like your friends who got really good interest rates but WAY overpaid for the car itself.
Then, you either kill the financing once you get to that portion of your visit, or you take the financing and pay in full that month ;)
Might not work, but if they are so used to people accepting ridiculous interest rates, maybe they'll think you are just as stupid and play along.