I don't think your going to find a NEW 08 IS-F for $42,000. If you do, it is going to be a demo with no options on it, and even then your not going to be at $42k. I have my Black/Black DEMO with 5,1xx miles with an MSRP of $62,160 that I'm selling for $46,500 thru March 2nd !
As far as what 949 "recommends" on doing, why make it that hard? Lexus frowns upon a dealership that makes it hard, and goes back and forth. Find a dealer you want to work with, pick out the car you want, drive it to make sure it's right for you, and if all is well, just tell the saleperson what your willing to pay. What's wrog with that? You can be suprised to see that you won't have to spend all day in the store, and everyone is happy. Just my 2 cents.
I don't want to say that your not getting that price, but I am going to say I see no reason to sell a Brand New 2009 IS-F at no profit. 2009's are very hard to come by, and production will not resume till May. Where are you located? In the Central Region, there are not Special Rates on the IS-F, unless it's a Certified Pre-Owned. I know talking to other dealers around me, we have seen selling them at MSRP or VERY close to MSRP on the 2009's.