Yes, you can do a year, or full residency, in int med. But you'll still need to apply for a FULL 3-yr derm residency to get boarded...
Candidates for certification by the American Board of Dermatology are required to have a total of four years of postgraduate training as described below.
a) The first year must consist of clinical training in one of the following types of broad-based programs in the United States accredited by the Accreditation Council for Graduate Medical Education (ACGME) or a similar program in Canada accredited by the Royal College of Physicians and Surgeons of Canada: a transitional year (formerly called flexible first postgraduate year), or a first year residency in emergency medicine, family practice, general surgery, internal medicine, obstetrics & gynecology, or pediatrics.
b) Three years of full-time training as a resident in a dermatology residency training program in the United States accredited by the Accreditation Council for Graduate Medical Education (ACGME) or three years of full-time training as a resident in a dermatology residency training program in Canada accredited by the Royal College of Physicians and Surgeons of Canada.
There is a few integrated int med and derm programs, but they're certainly not easier to get into than a normal derm residency.
Sorry, no back doors...