Me too on the sockets. I must have 6 or 8 sets. I tried some other stuff to use for extenders and none of them worked as well as your sockets. They are a bit of a pain but like you I don't sell them. I only use this mold every year or so and I hope I remember the sockets next time I decide to pour up a bunch.
Nothing else has worked as well as the socket idea. I have tried stage pouring, slow pouring, fast pouring and injecting with two different sizes of injectors. The sockets haven't made a worm with a void yet.