Hi Tempest,
Did you try setting him some humiliating tasks to do?
The exact nature of the task depends on how extreme you'd both like to get. Since you mentioned verbal play then I'm assuming you need to keep it reasonably mild.
Tell him he has to go into a store and buy women's underwear. If you want to ramp up the domination for this task he needs to have the shop assistant take a phone picture of him paying for the clothes. Note that he is allowed to tell the shop assistant any excuse he likes as to why he needs the clothes and a picture.
For example he could tell her the clothes are for his wife's birthday, and his best friend will never believe he had the nerve to go into a store and buy lingerie, which is why he needs the picture. It's a corny story, but it gives him deniability.
Another rule is that he should not embarrass the sales assistant in any way - and she does not need to be in the photo (she'll be taking it anyway).
As soon as he has the underwear the next part of his task begins. He has to send you the photo of him buying the underwear, and also a picture of the cash register receipt so you know the exact time he bought the underwear. Within fifteen minutes of the time on the register receipt he has to find a mens room, change into the underwear, and send you a picture that shows him wearing it. A good tip to give him is that he needs to become familiar with the self-timer and the macro setting on his phone camera
He needs to keep wearing the underwear for the rest of the day, taking pictures every hour and sending them to you as proof. Depending on his circumstances it could be quite a challenge to get himself into a mens room to take pictures every hour.
At the end of the day you have your webcam session with him and if he has complied with all the rules you could allow him to masturbate in front of you.
If you want to be cruel, let him start jerking off, and then stop him by asking questions or making up new rules. A couple of good ones are...
"Wait! I just noticed the third picture you sent was two minutes late. I guess that means you don't get to come today."
"Stop jerking off! The third photo was out of focus. You're a total fucking loser who can't even use a camera!"
Whatever you do to stop him, hang up on him, and wait ten minutes before you call him back. If he admits to jerking off anyway you'll need to think of a way to punish him. But if he's obeyed you and stopped then you could "overlook" his earlier mistake and generously allow him to continue masturbating.
Is this the kind of thing that might work? You can think up a whole bunch of different tasks, but I tried to choose one that is both humiliating, but also relatively mild.
Cheers,
Stanley
