I take plain white computer paper and take shreds and wrap up seads or nuts like a candy and put them in a seperate bowl for Dewey to work at, you could do that mini-sized for your cockatiel
Something like these might work too:
Happy Beaks - Round Feeder, Small
Teach Your Birds to Forage
Foraging / Treat Dispensers
I dont recomend the pineapple because its big, but the boats and bell and the candy apple should be fine and last a long time
The Beakery ~A Bakery "For-The-Birds"!