Wait... why are you feeding your bun sunflower seeds at all? Is your rabbit an outdoor bun or indoor?
You really do not need to give your rabbit sunflower seeds if they are indoors, and shouldn't as it's high in fat and only a treat food if anything - it should be kept to a bare minimum.
Rabbits should have a low fat diet as they don't really burn that much fat and store a lot of it - resulting in a tubby and unhealthy bunny.
I would suggest using something like fresh fruit as a treat and stay away from all seeds and nuts in general.
I see we all posted a tthe same time. hehe