First of all, your friend needs a lawyer. DWI’s can be serious, and I’m sure he wants to minimize negative consequences as much as possible (ie, get the best plea deal possible). Though public defenders are competent attorneys in and of themselves, there is definitely a difference in service between lawyers whom you pay an hourly rate for and “free lawyers”. The results may be the similar, but in terms of service, there SHOULD be a difference. If you can afford it, I would recommend it.
As for your friend’s situation, recently a CT court upheld a DUI against a driver who was only sleeping in his car while drunk. It comes down to what is the definition of the word “operation”. The Ct court held that turning on the car counts as “operation”. My personal feeling is that such an act does not fall within the spirit of DUI laws (ie, protecting people from intoxicated people from DRIVING), but that’s neither here nor there.
In NY, the law is almost as bad, but not terrible. Being caught intoxicated while sitting behind the wheel of a car that is running creates a presumption that the driver is operating a vehicle while intoxicated. The defendant can rebut this presumption by offering credible evidence to the contrary. Your friend needs to find witnesses that backs up his story. Maybe there’s a security camera somewhere that would support his story. Look for things that show he was in his car for a while and not doing anything. Oh, and of course, it should have been reasonably cold that night as well. It doesn’t look good if your friend said he turned on the car for heat, but it turns out to be a hot summer night. Build up on evidence, and that would give your friend a chance at getting off the charges. At the very least, the evidence creates a bargaining chip for him to negotiate with the prosecutors for a better plea deal.
Good luck with everything. Please give your friend my regards.