You could potentially use

Soit dit en passant

which is an idiomatic expression roughly equivalent to ‘I might add’.

The literal translation is:

Be said in passing

A few possibilities:

Il n’est malheureusement pas toujours sobre. Quand il ne fait pas carrément faux bond.

Il n’est malheureusement pas toujours sobre. Quand toutefois il ne fait pas faux bond.

Il n’est malheureusement pas toujours sobre. Enfin, quand il ne fait pas faux bond…

EDIT about carrément:

In this context, it’s to show the second case is ‘more something‘ than the first one:

Il n’est pas seulement grand, il est carrément gigantesque ! = He’s not just tall, he is a giant!

Note that it doesn’t mean ‘he is something + something else‘, but ‘he is not that, he is even more than that‘.

If I’m right, ‘Not only is he kind, but he also is beautiful‘ means ‘He is kind AND beautiful‘, but ‘He’s not just kind, he’s adorable‘ means ‘He is more than kind, he is [carrément] adorable‘. So I suppose ‘He is even more than kind […]‘ could be a good translation for carrément.

When I say more it can be more in different meanings: more… little, more… bad, more whatever. So you have to understand, for this case, that not coming is worse than coming drunk (of course it may not really be worse, but it means that sometimes he doesn’t even deign to come, compared to when he comes drunk).

Another usage would be an informal synonym of très : ‘Il fait carrément froid aujourd’hui !‘, same language than ‘You’re dead right!‘ (‘T’as carrément raison !‘). The first comparative meaning is probably implied in this second meaning. So you could say ‘Il est carrément adorable !‘ without any comparison with something less than adorable, and it becomes an informal way of saying really adorable.

I hope I made myself understandable.

Some suggestions:

To translate in the first place:

Quand dans un premier temps il ne fait pas faux bond.

Quand il ne fait pas faux bond dans un premier temps.

Quand, pour commencer il ne fait pas faux bond.

To translate we might add/I might add:

Quand il ne fait pas faux bond, pourrait-on ajouter.

Quand il ne fait pas faux bond, ajouterais-je.

Another suggestion:

Encore faut-il qu’il ne fasse pas faux bond.

Note that you also can replace quand by si in each suggestion.