What kind of apple are you trying to feed them? My suggies absolutely despise certain kinds of apple and can't get enough of other kinds.
also try cucumber or watermelon? Exotic nutrition's pellets work well but they don't smell enticing. Pocket Pets has delicious smelling food but it's outrageously expensive.
Grape Tomatoes are yummy too! AS well as grapes themselves.
You can try the Leadbeaters diet. but if he doesn't like eggs or honey he probably won't go for both together...