BPIMOM,
Welcome! Chapter 6 of AR 635-40 (found here
AR 635-40) contains the rules and information on COAD. This option would only be available after an unfit finding by the PEB.
Here is a link to AR 600-60, which contains the rules for MMRB's:
http://www.apd.army.mil/pdffiles/r600_60.pdf
I do think it is good to have an alternate plan to push for reclassification out of the MMRB. The issue that I have not looked at is whether you can go to recruiting now without the MOS. Do you know if he qualified for the Recruiting MOS? Has he considered just volunteering for a recruiting tour before going to MMRB? It may be possible to finesse this so he can gain time to heal and take the MMRB out of the equation (they could recommend referral to MEB). While in a recruiter billet, he could pick up the MOS at his NCOES level, if he has not already.
Bottom line, his benefits will be much greater if he can make it to 20 years. Whatever he can do to reach that mark will benefit him greatly.
Best of luck and please let us know any questions.