I did this for a long time before investing in the Bench Source Vertex. It worked for me.Get a cordless 3/8" drill and a 1/4" socket adapter. Buy a 1/2" deep socket and insert the case. Spin in the flame of a lp torch until you see the color change you want. Pull it out of the flame and invert it into a bucket of water. Repeat.
This works well in batches of a hundred or two.