You're really not just training your Sissy.....you're training your lover too!!!
It may take some time until he understands that your sissy husband isn't a man and so there's no "gay" thing about putting his cock in Sissy's mouth!!!!
It's really best if there's no lace and frills the first couple of times to get them both used to the idea!!!!!
And of course your big latex cock inside Sissy just hammers it home.....to both of them!!!