We are a specialty practice and we have one MD and one PA. Normally both providers are in the office together so we bill incident-to under the MD's provider number. Our physician is planning an extended vacation and we are facing the possibility of having to bill under the PA during that time and getting lower reimbursement. We share our office space with another MD, but he is not a part of our group. Our MD is asking if there is any way that the other physician could fulfill the supervising requirements for having an MD in the office suite. Could we consider him a locum tenens and still bill under our MD's provider number with the Locum Tenens modifier? My concern is that he is still seeing his regular patients at the same time.