Hi,
If you syringe feed him, feed him thru the rear side of the mouth, not thru the front.
Going thru the front can cause Aspiration Pneumonia, which moves quickly, and can be deadly. Feed a little bit at a time, then a little more. You can do the same thing with water, and stage 0 baby foods, such as, sweet potatoes, squash, peas, and chicken.
I find that olive oil is easy to give. I have never tried prunes.
Sweetpea1981 is correct. Put a dab on their noses, and they generally will taste it right off their wittle noseys. lol
Also, you can buy a bag of Carnivore Care. You can buy it online, or thru your vet. Mix some with water, and syringe feed. It will make your Dragon poop! It will be liquid, but, it will work. I have seen this personally more than once. Plus, it gets important nutrients in him.
Take care.
Emerald