Definitely check out the MSTP website listed above. Note that the suggestion to apply only to non-MSTP schools, is very much wrong. From my experience (F1 student at Vandy~MSTP school), as well as from friends I have at other schools, it seems to me that the better the program is, the more non-federal funds they have in their portfolio. End result: the better the school is, the less they care if you are a US citizen or not (a little counterintuitive, but absolutely true). Also, the better the school is, (with very few Ivy exceptions, the more they care about purely research and achievement, and less about "we have to have Americans" crap. Note, however, that being an outstanding candidate is a must since standards will be a bit higher for your friend, than for a Cit/Perm res. Also, a lot of schools quasi-pool their federal and local funds so your friend will be a part of the MSTP program even though he may not be getting the federal funds himself. At Vandy for example I know of at least 5 non-US students. One of the criteria for funding MSTP grants is to demonstrate strong commitment by the school for support of physician-scientists (or maybe more appropriately scientist-physicians). Hence the more money school itself puts into the program the better score they get (in addition to many other factors). At Vandy we have 10-11 fully funded MSTP students, but the MSTP grant gives enough money for 5-6 (i think), the rest are funded by the school. Do we know who is NIH funded? From discussions with other students I do not think so, the school does their thing and never tells you, as you are all part of the "MSTP" as they define the program. The only reason I know I do not get federal funds is because I cannot. Interestingly, until I joined SDN last year I've never even heard of the MSTP/non-MSTP mudphud concept. Soo.... my point is, it is certainly possible, and at some schools even encouraged for those who are committed to a physician-scientist career. Focus: research, that has to be undoubtedly the most most important part of your application. Depending on the school, I am almost tempted to say that "traditional" med school values such as volunteering, etc.. are, well, not irrelevant but not stressed. So, when in doubt do your utmost to get published and noticed by research faculty, clinical MD recs are not nearly as important.
Very best of luck to your friend,
Aleks