Potential target training difficulty

I would liike to solicit the advice of the experienced target trainers on this forum regarding a potentially challenging bird.

I am in the process of finding a bird to adopt from a local rescue. One particular bird that I am interested in is a 10 year old Sun Conure named Jack. He is a very friendly and outgoing bird who will go to any one, and is even happy to accept scratches from complete strangers. The catch: even though he has no apparent fear of hands, he will not take food or treats from the hand. His foster mom says that this has been the case the entire year that she has been caring for him. He was also not inclined to take a treat from a spoon or popsicle stick when I tried that, but he may simply not have been interested in food at the time of my visit.

Is there any way to overcome this trait? If I were to adopt him, I'd want to target train him just like my other bird, and his refusal to take treats would make that a bit difficult. Any words of wisdom for training such a bird?

He is an engaging little guy and I have made arrangements to visit him again soon. I'm just wondering how I will go about training him if I decide to bring him home.

When I first got Brady she would not take food... well the kind I wanted to give her any way. Show her a chip or a piece of popcorn and she could snatch from your fingers like a kung-fu master. What I did was give her a tiny and I mean tiny piece of chip then give her a pine nut right after until she started taking pine nuts or other nuts like walnut and pecan pieces with the same sort of enthusiasm as the chips. Now she gets no chips and doesn't realize she was out witted.

I should add that this took a little time, at first she would toss the pine nut back at me or any other good for her food. Now she will take most things, nuts, grapes, she still throws pumpkins seeds back at me!

My gcc doesn't take treats from my hand but will target train... He loves verbal praise.