Depending on where you study, picking up some of the pre-med coursework in summer school can be very easy. Of course this would restrict other summer activities a bit, but it would give you more flexibility during the regular academic year. You also could investigate a couple of the post-baccalaureate pre-med programs as ways to cover any missing requirements after finishing your music major. Yes, this would add on a year to your total program of studies, but would not necessarily need to be a full load for that year.