The best tool you can use when negotiating is knowledge: dealers thrive off of idiots, which is the vast majority of the buying public.
Don't base your logic of 'most people are able to get them 3k off invoice' off of what you read on this site. Edmunds.com's True Market Value is actually a very useful tool in finding out what you should pay since it essentially gives you an average price calculated off of what everyone else is paying. My future order combo (Inferno Orange 2SS w/ RS) MSRP's at $36,120 but the True Market Value according to Edmunds is $35,819 - that's the average price paid.
Try using it and bringing it to the dealer.
www.Edmunds.com