There's no special coding you need to do for this situation. If the secondary payer has current information from the patient about their Medicare coverage, then they should already know that if the patient only has Part A and that the physician services are not going to be a covered service under that patient's Medicare, and they should process the claim accordingly. In fact, I don't think you would even need to bill the services to Medicare and get a denial - you should be able to just bill the secondary payer as if that was the patient's only insurance. If the insurance is doing their job correctly, they should not need to see a Medicare denial for every claim.