You can always just shake a can of pellets. ALL of my animals come running when it's feeding time, whether it's their food or not. And by all, I mean the rabbits, dogs, cats, horses, sheep, chickens and guinea fowl. My pond fish follow me around while I walk past the pond, hoping I drop food but they know if I stop and they see the can, they will be fed. =D Same with my aquarium fish, they see the can and race to the top.
Getting rabbits to associate a clicker to food would be easy.