However, I suspect your goal is more likely to help him get himself back together after his traumatic break and out there in the market looking for another Domme he can serve in a maybe more sexaul manner.
Yes, this is my goal. Right now, actually, his goal is even less specific than mine; he says he just wants a girl, even a vanilla one. He's brought over a couple of prospects for my inspection and approval, but so far none has worked out (I told him to stop acting so desperate, but he's horny and heartbroken so really he has everything going against him). It's tricky because our circle of friends is pretty tight, so whoever she is has to somehow get along with me (and I don't get along with other females so well; they usually try to have opinions different from mine).

With this in mind, I would consider controlling things like his clothing, his appearance, his diet etc - make him a more attractive prospect for another Domme.
Done. Fixed his hair, taught him how to bake cookies properly,giving him instructions on what to say in order to get first dates (he's actually succeeded at that, now).

However, I would be careful not to alow him to get too attached to you to the extent of considerng you to be his Domme. For one thing, he may not want to find another Domme because, in his mind, he already has one.
I'm not too worried about that. We've been friends for years, he went to high school with my sub, and he's not getting anything sexual from me. I'm basically just his emotional support as he tries to get himself back together. If he was my vanilla friend we'd just take him out drinking.

Telling him what clothes to wear is an excellent idea; I don't know why I didn't think of that- I already control my sub's entire wardrobe, but that's one of those things that's just so usual you forget to think about it.

As usual, fetish, your ideas are very helpful, thank you.

And yes, denuseri, he needs additional training, so maybe this is a good thing in the end.
His hair really was awful.