Hiya again! Bed time here :-) Go with your gut on this one, G. A 'name' email is the right place to start. You won't regret it. And it will probably open up more positive communication - for eg. about how/when he meets her. Given all that, I would do it any time soon. Time flies in the last month of pregnancy and your WH might need a bit of processing time?
Also I don't think you are likely to get the "I think that is wise, since we'll be divorced soon' line... can't say why, but just don't feel it from here... Hey! but what if he suggests his name be included - are you open to the idea?