I find that nut and seed butter works well with Noah. The brand I got is human grade without any sugar or salt added, and it's called "Nuts for Nature." It's peanut-free and probably has lots of vitamin E, minerals, and B-complex vitamins. I'm just assuming this based on the ingredients since foods that aren't fortified don't list such vitamins, minerals, etc.
You could use a bit of honey, but I definitely think organic, human-grade, no salt or sugar added nut and seed butters would do a better job and would be healthier for Oliver. Plus, by mixing a bit of nut or seed butter (NOT PEANUT BUTTER) into his pellets, he'll consider pellets to be a higher value food item given the amount of (healthy) fats and protein present in the nut butter mixed in. Parrots place higher priority in consuming foods rich in fat and protein, rather than foods that are low fat and low in protein, even if the low fat food is a powerhouse of vitamins and minerals.
Speaking of which, if your bird won't eat their healthy veggies, you could always purée it into a baby food consistency and mix some almond butter into it or something.