BS-they get a discount PER CAR, they shouldn't have to split it. At a MINIMUM if you push for it you'll get their advertised price, and you may well do better, especially considering the punch date. In addition to my deal, three other guys on this board got similar deals, look them up in this topic--Jim Patterson, Rafale, and rolf-dieter. You can find everyone I think in the "sanity check" topic, or search their posts for their deals.
$10k off is the MINIMUM you should expect and you may be able to do better. Talk to Jim Patterson, he's in your area, he might have seen other deals. My dealer in CT had a couple of other Z4s similarly discounted, worth checking their website too, or look in the "blowout prices" topic for a link to their ad.
Because of the punch date, you should also expect them to extend the warranty by 3 months/5k miles; this is often done for a car with an already-running warranty. You hold the cards here, the longer the car sits on the lot with the clock running on the warranty the less valuable it is. Punching it really jump-starts depreciation!
2009 Z4 3.0i roadster
Sapphire black, beige leather, premium, auto, comfort access, cold weather pkg, Sirius, sport, alarm, ipod & smartphone integration
BMWCCA member #402504