Well, one or two of them are in public but are not public humiliation. The trouble is that I get the impression from the post that he is not being humiliated enough by what is already happening so things need to be taken up a notch to keep him on the edge of his comfort zone. The tied balls, for example, is in public but is rather discrete. You can't see it unless you are specifically looking. Likewise, you can set a level of the shopping task that is not so public. At the lower levels it is concievable that he is merely buying underwear/make up for a lady not for himself. As I said, you start small and work up until you exceed his comfort level by a small amount. The 'serving at parties' thing is also generally a very subtle thing and is mostly what a good, polite partner should be doing for thier lady (well, at least in an old fashioned sense anyway... rarely see it these days but it is still not all that unusual as to be commentable).

About the only things on there which are overtly humiliating in a 'yes, this is BDSM that is going on here and even those who aren't in the lifestyle can see that' sort of way are the feeding one and the later levels of the shopping where you actually try things on and ask assistants for help. These are overtly BDSM because there are very few plausible excuses you can use to justify them without referring to the lifestyle (a costume party/Rock Horror show may cut it for the clothes but it will still raise eyebrows). I've found with my personal experience of public humiliation that it is easier to take if you have an excuse.

A few more ideas you may consider (these ones more private)

- Marker pen to write things on his body. You can write anything you want (My property, my slut etc) on any part of his body and it can be covered with clothes.
- Put a pair of your used underwear in his bag before he goes to work for him to find. You can also do this with notes and other things - for example his collar, a vibrator you used on him last night, the silk scarf you tied round his eyes. It is something that will make him remember you and/or a specific session and maybe blush a little at the memory. A photograph of you is also a good one, preferably naked or sexily dressed. This is especially good during periods of chastity for him. The idea is that he finds the object and it catches him off guard but people at work are unlikely to see it. Later in the day, send him a message or ring him to ask if he found 'your present' to him. This is just in case he hasn't bothered to look in his bag yet...
- You can send him commands and instructions while he is out/at work. E-mail, text message, phone call etc. Make sure you use a non work resource for this. Also, use your own discretion as to what you think he can get away with at work without getting fired. Commands sent to him in this way could be to do immediately (i.e. 'go to the toilet and masturbate until you are on the edge then stop and report') or could be to do later (i.e. 'I will be out when you get in tonight. When you get in the door, take all your clothes off then go to the bedroom. There will be further instructions for you there.')
- If you have a walled off garden area, you can do some nice things in the garden. Do more or less what you have done already (dressing him etc) but this time in the open air.
- Even if you do not do the shopping task, I still think it is time he had his own collection of clothing so that he is no longer borrowing yours. At the very least he needs a full set of underwear, a skirt, a top and some shoes. And probably at least one pair of panties a day. You can instruct him to acquire these but leave it up to him how he does so (the easy option is to browse ebay as there are a few spe******t TV shops on there or look for other online resources).