I'm convinced of your explanation & genuinity of the reason that you put forward ...I hope the CIC official will feel the same way too....
but anyway,no harm in politely asking ur ex boss if it is possible to get it done..we generally underestimate people & how generous everyone are,given a chance (talking from my experience regarding my experience reference letter)..
so give it a shot,ask him if it'd be possible to do so,and even otherwise if if you are supplying with all the other contact details of ur ex boss,then I feel it should be fine....
(I'd approve your case if I were the CIC official... however these days Oinp ppl will be getting many such letters as their documentation is stringent and I'm sure each and every profile will carry such letters...so we can't predict their mindset...
so give notarizing a try,if not go ahead with what you have got....
All the best to you....