I bought my keets a birdy kabob toy; short sections of bamboo filled with soft wood, strung on thick fibrous twine. I tied it to hand vertically in the cage, and at first they weren't interested. Then, I laid it horizontally on top of the cage, and they are all busily picking at the wood. They have got one section hollowed to the depth of an inch in about a day.
Busy birdies!