we took in 3 gliders awhile ago.
gave them Hpw with fruits and veggies.
they ate the HPW ok at first. but barely touched the fruits and veggies for
about a week. then it was still a MONTH it seemed like before they really started eating well.
NOW they spit the HPW all over the kitchen walls, and I give them slightly more then normal HPW since they eat it all.
some veggies, like green beans look uneaten sometimes but the center is gone, same with some peas, seems like some are good at eating inside and leaving outside untouched.
you could get some gala apples and try to hand feed them a peace or too at night. our stuff is all frozen so sometimes I give them fresh and they like it better.
Glider drink only a little water, they get most hydration from food.
Note: unless he is sick, I think it is very rare that an animal will starve himself to death.