Personally, I shadowed an pediatric MD last summer for about a month. Thus, he knows me faily well, and I asked him for a LOR.
To satisfy the DO letter requirement, however, I asked a GP DO that my mother's side of the family has been going to for decades to write a letter. His only connection to me was that I knew him in that aspect. He didn't have a problem with it, and is currently drafting the letter. Because he doesn't know me all that well, I gave him a CV and a copy of my personal statement to use for the letter.
I did this in hopes that I can demonstrate a history of shadowing and clinical experience (beyond my hospital volunteering) and that I can also demonstrate a knowledge of the osteopathic profession...we'll see how adcomms like it haha.