I agree with Dan, the best way to improve your creek skills is to try hard but lower consequence moves. You're already running the Green, so you have all the tools at your disposal. Find a good boater and have them show you the "alternate routes." You'll be doing all sorts of weird slots, boofs, peelouts, and ferries before you know it. The key to creeking is precision. For a good line on big boy creek drops (Gorilla and Sunshine are good examples) you need to be able to put your boat in exactly the right place with exactly the right angle and take exactly the right stroke. Big rivers give you more leeway in that regard.
Get your boof dialed and learn to read drops to know what kind of boof you need: straight, flared, late, stomped, etc. Luckily, boofing is one of the funnest things you can do in a kayak, so the learning is usually enjoyable. Again, you've got a sick training ground in the Green. Take advantage and watch/ask the good boaters for technique tips. If you're styling the whole Green on the regular, then your probably ready to step it up onto some of the badder stuff in the area.
"A river is more than an amenity, it is a treasure."
-Oliver Wendell Holmes writing for the majority in New Jersey v. New York