If that doesn't work, feed them nothing BUT fruits and veggies for a little while. Gliders are like 2 yr olds, and sometimes you have to make them eat what's healthy. They may stick their noses up at it for the first or second night, but then they will get hungry enough to begin eating it and once they begin eating it they will start to like it.
I went through this with my two new girls a couple months back. They loved their fruit and HPW but wouldn't touch their veggie relish. So I drastically reduced the amount of fruit I was feedng them (one tablespoon per glider to less than half) and still gave them the proper amount of veggie relish. First couple of days the picked at it but when they realized nothing else was going to come their way they got serious about it. Now, they LOVE their veggie relishes and clean it up even though their fruit portion is back to where it's supposed to be.
I'm a firm believer that you can make any fickle glider eat well, provided you are more stubborn than them. When they are refusing to eat something healthy for them it's usually because they are filling up on other stuff. Take away that stuff and you'll make them not only eat but adjust and develope a taste for what they were originally rejecting.