Sounds like an ideal opportunity to use your trust old friend the DO ( Demi-Official ) letter, as per JSP101 - making any amendments that you know he favours. In my humble opinion the one Milsum has posted is slightly incorrect. I doubt, however, that you would be approached by a mess steward with the mess webley on a silver tray.
In my experience there's no need for it to be handwritten - I'd save that for Formal Letters i.e. "I have the honour...."
Obviously you should chat through your reasons with him beforehand - the letter should simply act as a formality to be passed on to Bn HQ / MCM Glasgow.