doh! lol. ah well... worth a shot at mentioning it. i think i have one of those too 'cept she's a she. she's scuffed baby bun's eye twice now and i can't risk her doing it again... poor baby bun. i'm trying the stunt double method with moderate success. how hard are the nips? have you had any wounds to tend to? do you hold the nipping bunny's head down to show dominance after they nip? i think sometimes nipping is okay if it's not doing harm but i get that you want to see progress.
markusdark's maryann was quite a feisty bun and nipped a lot at her bunfriend dono when he was trying to bond them. i *think* that the bonders he took the buns to thought that she didn't know acceptable bun behaviour and needed to be taught it. dono was too afraid of her to teach her. (correct me if i'm wrong markusdark!)
i also watched a youtube vid about bonding where they said a similar thing. in both cases the bonders set up the bonding area so that there was a separate spot for one bun to goto when they've had enough of the other bun's behavior. in the video the narrator said that the older more experienced bun would go into the crate and face out & not let the younger bun in or near if the younger bun did something unacceptable (like too much humping or nipping). this eventually taught the bun what not to do the offending behaviour.
does your bonding area have a 'nook' in it where one bun can retreat to? how big is your bonding area?
i may not have any good solutions but answers to some of these q's could help some one else give advice. i'll be following along your thread to read suggestions for sure!