Blah irritating bird

So I've had Echo since he was eight weeks old, he'd be about 7 months old now and I'm still having trouble convincing him to eat veggies. He eats corn no matter how its cooked, creamed corn, raw corn, popcorn he'll eat all that and he might have a taste of carrots now and then but otherwise he doesn't touch veggies. I'm fairly sure a seed and corn diet can't be much healthier then an all seed diet so any suggestions to get him to eat more veggies? I've tried mixing corn with other foods and though he'll taste the new foods, he'll never take for then the tiniest nibble.

Right now he has his seeds most of the time but at dusk when he usually eats a lot we've been taking his seed away and giving him veggies, doesn't seem to do much except make him hungrier in the morning.

What veggies do your birdies go running for?