If you can't see what he picks out to eat, you could try putting the food into little piles next to each other on a saucer and see what he picks. I would do this first thing in the morning before he gets anything else to eat, it is when he will be the hungriest. I would also not use the seeds in this process, in fact I would hold off on giving him the seeds until his evening feeding.
When you feed him in the evening use his seed and a mix of the thing that he didn't choose. The next morning again use small piles of the foods that he didn't choose and then feed him that evening with a mix of seed and the food that he has chosen. New foods in the morning and the foods that are chosen in the evening. Try this for a while.
Let us know what he chooses.






