Since nobody here really answered your question, let me tell you, as long as you don't just write for immediate family members, you keep up to date with your CE credits, and you stick to what you know, then, yes you can do it part time.
I have a client that runs a Disc Jockey service for weddings, parties, and company picnics. When he gets overloaded, he calls me, and for 4 to 6 days a year, I am a disc jockey. I am good at it, and the people enjoy my personality and selection of songs. Does this make me a disc jockey? No.
Does it mean that I cannot do it? No.
I believe in multiple streams of income. That physician example gets me everytime. (yuck, yuck) As long as you do it, do it well and abide by the ethics, then I see nothing wrong with it.
I have an associate who is the drummer for a musical act (Hittin' The Web with Donna Hopkins :: Where Music Plus Friends Equals Family
). During the week, Richie runs quotes for agents like myself. And, on the weekends, he plays drums. Gets paid for both, and is excellent at both.
Part time doc...tee hee hee