Boom! Sorry for the dealy - had to be afk for a few.
This is exactly what I was after, thank you @sam for the code and @Dannii for the translation 
So next related question: is it possible to insert a link? I know we can edit templates, but does that email customisation have access to the reply key? So href=mailto:[reply-key]@[domain]?subj=[subj]&body=watch ?