Some cut logs at different lengths set on end give them something to hop up on.
Instead of a level roost made out of a piece of lumber, you can try to find a tree limb that twists and turns and use that as a roost/climbing gym.
I like the head of cabbage that flockwatcher mentioned. Just hang it in the run just above their heads so they have to work at pecking it. They'll play with it for hours.
If you use wood chips in your coop, throw a handful or two or three of black sunflower seeds in on a rainy day. They will spend the afternoon scratching through the chips to find and eat them.
You might also want to consider building a salad bar in a section of your run. Build a frame out of 2 x 4's, cover it with hardware cloth, plant grasses under it. The chickens can pick at the grass as it begins to grow through the hardware cloth, but they can't destroy the roots.
Spend time with them, even if it's to sit in a chair outside the run. They love having you around.
Jim