Not a group buy, but discussed buying 2 cars back in November when I got my CR-V.
The dealer is a friend so I asked what he could do if I wanted to buy both a CR-V and an Odyssey at the same time. He said that on the cars with limited availability (CR-V, Odyssey, and a few other select models/trim levels) he had one price for return customers, multi-car customers, and friends. Everyone else gets MSRP he said.
He looked at his pricing sheet and wrote numbers on the CR-V and Odyssey brochours and handed them to me.
Since I don't live there any more, I think that he thought I was just getting amunition to negotiate with a local dealer.
When we changed our mindes to the Pilot, we got the same percentage off, so I am guessing it is a flat calculation.
I would think most strait shooting dealers (There are a few) would do about the same.
Find a friend that wants a Pilot, Odyssey, CR-V, or (S-2000) and have them go in with you. Or just buy an extra car for your wife/kids/parents/(self).
I am planning to ask the same question on the Pilot in a couple weeks. I already bought a car last year at MSRP (Subaru WRX) from the same place. I will see what I can get out it. Since it happen last year I may be out of lack.