Cold turkey may be the best. Gliders are picky. As long as their previous food is in the cage then that's what they are going to eat. They most likely won't eat the critterlove complete for a few days. It'll take time but they should be able to switch.
As for the salad, I think it's great in theory but I don't know of anyone's gliders who actually early it. My glider's won't touch bok choy and only are the corn and peas.
You are better off giving them the ingredients separately and fresh. So instead of them getting everything at once, give them one fruit and veggie they like that's on the salad list. So far it's worked for me.