that would be harder...one you will have no letters from the specialty...most programs will want an LoR form the Chair of the Dept (or at least a letter form an attending in the field) and two it raises the question...how do you even KNOW that you want to do the specialty if you have had NO exposure to the field.
my advice to do an elective, even if its only a 2 week one or while on a different rotation, go spend time with someone in PM&R during your off time.
Endocrinology, Diabetes and Metabolism Attending
ABIM certified IM
ValueMD-the place "where nothing makes sense, but everything is related-fellow vmd'r gabon