Can a (properly rated, ie. FI/MEP) instructor sign somebody out to fly a MEP solo, without a license[sic]?
Yes.
Just trying to workout why it's a minimum of 105 hours
Because I wasn't concentrating when I made the last post! You are quite correct, of course
No, BillieBob, he was not a professional pilot
Ah, when you referred to "appropriate exemptions for his considerable previous military experience on both single- and multi-engined", I sort of assumed that he was a pilot. In any case, it does not change the fact that he did not undertake an ab-initio PPL course in a twin, which was the subject of the original question.