There are quite a lot of recipes on the forum, there is a thread called 'Chocolate Paradise' that you can search for. Quite a lot of the recipes have ground almonds in them (otherwise known as almond flour) and artificial sweeteners in them. You will have to check he can eat either of these as some people are allergic to nuts and some artificial sweeteners cause an upset stomach.
It is nice that you are thinking of him, but on special occasions he may just want some of the ordinary food,
I'm not putting a downer on your good idea, but maybe a voucher for a trip to the theatre or something else he likes doing would be a better present than reminding him that he has diabetes on his birthday.