Hmm, still seems to be missing something. Nothing seems to have changed
Greetings. Sorry it took a bit to get back to you on this. I found a slightly more elegant solution than what I was previously suggesting.
Since I already went to the trouble of testing it out myself, I already have a patch file created. Simply load it after the crafting system plugin and it will hide the fourth slot, and skip over index 3 on the list.
It can be downloaded from the Crafting System main page, labeled as the three ingredient slot patch.