In re-reading my response, I realize I was not as straightforward as I could have been. I used your term sole proprietor in my response only because that is the term you used. Note that Medicare distinguishes between sole proprietor and solo practitioner when it comes to NPI Numbers. I was questioning if maybe the Medisoft Tech Support had some reason to know that your client is actually a practitioner. If he is, that would require an answer different than if he indeed is a proprietor (folks sometimes don't know that Medicare sees a difference between those two terms).
Do you know for certain how Medicare has your client set up - proprietor or practitioner? If your client has not established a legal entity through which to do business (corporation, partnership, LLC, etc.), he should be set up with Medicare as a proprietor, not practitioner.
If you already know this, then nevermind.