You might try eating with him, or eating the sme thing you give him at the same time. Some people recommend just giving the fruit and veg first, then the seeds and pellets after they have eaten the fresh food. You could also try hand feeding new things, if he will take them, then at least he might try them.
Have you noticed which fresh foods he likes? I pretty much had to keep track of likes and dislikes, and when one liked broccoli, I'd add in things related, like cauliflower and brussels sprouts. My zon has never eaten citrus or most berries, but loves starchy things like corn and peas. She will eat very sweet grapes if I cut them in half.