This might be obvious to most people, but:
You only need one ground wire coming out of your encoder, they can all run like christmas lights off the same wire, going in and out of each switch. You can see that in all the pictures above.
And yes, I *have* seen pictures of people who jammed one ground wire into their encoder for each switch - that becomes messy really quick.
Was that me on my first attempt? I can't remember and this picture is so frenzied that it's hard to tell if that's what I did (either way - don't do it):

Joseph Elwell.