I think it is possible in some programs, but it may be harder to accomodate in others. It would depend on several factors: whether you take grad courses in first two years (and how demanding they are), the demand of the med school curriculum, and, most importantly, how much you are willing to work. There are some people that choose to do this, and it's feasible, but it may be a little more difficult at some programs than others. Personally, I think med school, grad classes, and slacking will occupy most of my time 😀.