I hope it's not too late and I can share some knowledge. Your buddy will need to read the Army Regulation, and become familiar with it, because his chain of command will have no idea how to handle it. Here goes:
1. Your buddy can submit a DD368 to be released, if appointed, and sent to the Academy. This is very straightforward. However, I don't recommend it. Why? Because then the costs of moving and everything will be on it. The military will not pay for anything.
Or
2. Refer to AR 612-205. It's pretty straightforward. However, I will point you to the meat of it: Page 4, Section I, sub-section 4, paragragh d:
"Unit commanders will issue PCS orders for active duty personnel to attend USMA or USMAPS."
The AR is a few pages long so print it out and read it. While the regulation focuses on West Point, it also mentions "service academies" thus the AR applies to USMMA also. USMMA is in a unique spot. It belongs to the gov't but it's not fully, fully considered by gov't agencies as a "service academy". If you don't believe me, google it. However, for purposes of your buddy's transition, AR 612-205 will suffice.