Fresh foods are more important than seeds. It's nearly like the difference between eating a healthy diet vs junk food in humans. Try dicing the pieces up real small, maybe offering them in cooked rice, leaving some veggies whole and hanging them from the sides of the cage or from the top, maybe even buying a metal skewer and putting the foods onto that and then hanging it in the cage. You can try eating the food right infront of them and making 'yummm mmmmm' sounds as if it's the best thing you've ever had...
You need to be persistent and keep offering fresh foods in as many ways as you can think to prepare them or serve them. You might want to think about supplementing with pellets (if you'd have any luck getting them to try any), and also feeding germinated seeds, just as tails begin to grow (but no longer or else they'll become sour or stail tasting). Feeding germinated/sprouted seeds is another great way to offer a variety of nutrients that are not found in dry seed. You could also try sprouting beans, various types of seeds, and grains. Check out
http://www.sproutpeople.com for some great mixes!