My first rabbit was bit by a poisonous spider (in the house) and her face started rotting out. Once it started to heal with meds, she wouldn't leave it alone, leaving a red, bald spot. The doc first gave me an ointment to put on it, to help it heal and to discourage her. I don't remember what it was, but you can call and ask your vet for a recommendation. It didn't work. He had me then put a cone on her
It worked, but she looked so sad in her cone. As soon as a little bit of hair grew back, I took it off. Once it wasn't bald anymore, she didn't obsess with it.
(If using a cone, you will need to re-think food dishes, etc, unless you just want to put the cone on when you aren't around to stop the grooming.)
I haven't had bonded rabbits, so I don't know if this is possible, but could you separate them for just a week or so? That would probably do the trick. Maybe side-by-side cages with supervised play (and you removing them if the one starts to groom the other)?