Idea one: We did buy some of those "habitat defined" foraging toys for Mango, our GCC - not too much smaller than Skeeter. We got the one with drawers, the one with pull strings, and the one with a swinging door. One took him a day to learn and one took a few days of disinterested poking before he finally got it and now he's a pro at all three - BUT that's not the point. We use all three in his cage to feed him his supplemental Nutriberries (sometimes we'll use all three at once, take one or two out, etc). We re-position them everyday (and his cage is pretty large) so that he has to find them and then use them to get one little chunk serving at a time. They're weak toys, yes, but he seems to have no intention of destroying them, plus the repeated activity of finding the toy and using the toy over and over to get his servings is really the essence of foraging for food. His Nutriberries are his favorite bits so he's more than willing to work hard to get to those!
Idea two: In addition, we have two cheap plastic food cups (also the kind of budgies) that contain the rest of his diet, his Roudybush. Those also move around the cage to different spots everyday and we also sometimes sprinkle shreds of crinkled paper over the food so that he has to throw the paper out and/or dig through in order to get his food.
This is a really, really easy way to increase the mental stimulation of your parrot. Don't use the food dish holders that come with the cage - just buy some little cheap ones that hook onto the bars and move them around every day - plus add toys or paper on top of the food and BOOM: foraging stimulation.
I really like the paper seed tube ideas! Although Mango hasn't really shown interest in tearing through cardboard or coffee filters to get food, those might be easy enough to keep his interest and still give him something to do...
We're working on finding more premades/devising little toys to eventually have Mango feeding exclusively through foraging toys & activities in order to give him the most stimulating environment possible - since, of course, parrots in the wild are not so lucky as to find all of their food in a convenient little metal dish next to their water

A parrot that has to work for its food while you're away is a parrot that is not getting fat or plucking feathers or screaming all day.