Take your Sissy to the spa or salon and have him go through a complete makeover with full spa treatments. Have him get a facial, wrap, eyebrow trim, body scrub, etc.
This will make your sissy feel like a real girl getting real feminine treatments, and more over it will publically humiliate him in front of the other women who are performing the treatments or who are also in the salon.
Tell him its time for him to have some special treatments done that are specifically for a sissy like him.
Bring him to a salon or spa where you know there are a few young attractive women who are willing to do give him a bit of a makeover and have fun with it. Before going to the spa make sure he's wearing both a pink bra and panties, and that you have him wear a feminine blouse and some pants that could easily be mistaken as feminine as well . Load him up with some female perfume, just before entering the salon. Make sure he is wearing his chastity device (very important) and you should be wearing the key. Tell the women at the spa to take him and do as they wish (nails, pedicure, bikini waxing, facial, etc) and not to hold back. Be sure to take pictures of the whole process!
Do this on a special day, when you want to surprise him. Have him block out a few hours in his schedule, then take him to the spa. You may consider leaving him at the spa and meeting a date for a few hours, telling the staff of the salon to keep him busy for a few hours because you have a date at home and you don't want him back until a certain time. Alternatively, you may want to have fun and do some spa treatments together with him.
The women at the spa will almost certainly catch on to the situation, and they should have a good laugh. Remember that young attractive women are the most intimidating to be humiliated by, so try to seek out a salon with such type of staff. Let them have fun and take pictures of his predicament.... this is all about public humiliation!
Make you don't involve any other men, as it would be a total turn off. Also, don't be afraid or embarrassed…. This situation is to embarrass and humiliate him, that's the point.