I bought a set of these 3-inch wooden balls from Amazon, went to Home Depot and bought a pair of #0 size Eye Bolts similar to these and screwed them into the wooden balls. Total cost, roughly $20.
Then I simply hang them from a short nylon runner and a mini biner and do hangs off them. If you hang directly underneath and keep your fingers below the center line, you'll work your pinch grip pretty hard
Also, you can pick up a 3-4" PCV pipe and run a rope or chain through it and hang underneath. Like in this video.