Have you tried a dressing that includes the use of a cohesive bandage ?. Even if Bunny gets it off eventually it will take some time to do so and thus allow the cream to be absorbed first.

One word of warning about the ingestion of Sulfadiazine cream. Until very recently I had used it for years on numerous Rex Rabbits who are prone to Sore Hocks. But last year one Rabbit developed neurological symptoms shortly after having the cream applied which he too kept licking off. We cannot say for certain that the neurological symptoms were due to sulfadiazine toxicity, he was treated for EC as a precaution. But the symptoms were seizures and ataxia which lasted for about 3 days. This side effect is apparently very rare, as I said I had used the treatment for years on numerous Rabbits with no issues. But now I would be very wary of using it if the Rabbit was constantly licking it off.

Perhaps the Vet could add some lidocaine cream to mix with the Sulfadiazine. Lidocaine Cream is a local anaesthetic.