How about preparing a detailed "Purchase Order" type document with all the options, etc. that you want for you car, then getting a list of dealers and the "Fleet" contact persons. Then, you email/fax your PO and tell them that you are doing a competitive offer and whomever gives you the lowest price gets the car bought from them.

Whittle that down to 5 dealers, try to play them off each other, and then go to the lowest dealer. I wonder if this approach would get you close to or below the $500 over invoice.

I read of this approach from Fool.com: Stock Investing Advice | Stock Research