I could only imagine the look on the dealership's faces if I took mine in for warranty work...

1. Develop a relationship with your dealer. Get to know a couple of people by name. Not salespeople, they are a little to "transient" and have almost zero clout. I've had vehicles worked on (under warranty) with Nitrous installed. You'd be surprised what they'll do for you if they know you...
2. If it's a part that is under warranty to begin with, have them do it the first time. Then, you're covered. I know, we like to do our own stuff. But, if you need the warranty, stick with having them do the work until you're out of warranty.
3. If you don't want to use them, don't complain when they don't want to pay for it. They get paid for the Service work and appreciate the work for the Techs. Probably a better margin than on parts, anyway.

Just my .02



Rich