Train him how to wear a bra…making it like a (humiliating) lesson….like the first time a teenager girl wears one.
Makes him practice taking several on and off in front of you. Give him 5-10 things he needs to know about wearing a bra, and then makes him memorize them and repeat them back to you when you quiz him …(like, 1) never let the straps show, 2) always choose a color that doesn’t shine through, 3) always be sure the bra matches the panties, 4)….etc). Make sure you quiz him when he least expects it, and give him a humiliating punishment if he should forget any of the rules you’ve instructed him with. You could even get a girlfriend to quiz him for you, which would be absolutely humiliating!
Insist that he wear a matching bra and panty set at least 2 days out of every week, all day, no matter what he's doing. If we wants to be a sissy, treat him like a sissy and enforce him to wear these very basic feminine items. He should actually be wearing woman's panties every day, without exception.
Pick 2 days out of the week (like Monday sand Wednesdays) and enforce the rule of having to wear a matching bra from the moment he wakes up, to the moment he's ready to go to bed. Rub our hand over his back now and then to remind him you know he's wearing a bra, and also to check that he has it on. It should be his responsibility to have it on always on those two days, and if you ever catch him without it you should enforce a swift and very strict punishment.
You can punish him for not obeying by making him wear one 3 days in a row, extended chastity, not letting him wear shirts that will cover it up, or the best is to make him tan 3 times in a row with the bra on so that he'll have tan lines to remind him.
The point is to show him you are willing and able to enforce him being a sissy more than he wanted. By you over insisting and enforcing this, he's not only humiliated, but he's reminded on a regular basis of your feminine authority and his ridiculous status. You are teaching him a lesson to be careful what he wishes for.
Have your girlfriends give him a surprise 20 second backrub to him when you he's wearing a bra under his shirt….
Try to seek out any excuse to punish him and keep him alert when he least expects it. Surprise him by opening his shirt, and asks him where’s his bra?. Then explain to him how he will be punished, taking out a note pad and clearly noting the incident so that he sees you will not be forgetting about it later.