"Do not attempt home treatment until a veterinarian has positively diagnosed ear mites in your pet. Ideal home treatment includes keeping the ears and the rabbit's habitat as clean as possible. Only use ear cleansing products designed for use in rabbits." (answerbag.com)
Someone did mention mineral oil (in the link provided). Although, it's probably best not to take a chance of hurting your bunny if you are not quite sure on how to do it properly.