“Split” Cat 5 network cable

I know I have read or heard somewhere that it is possible to “split” a Cat 5 network cable and make another connection using the 4 unused wires but now that I need it, I can’t find it anywhere. Could someone please tell me where to find detailed instructions on this?? preferably someone that has actually done it. I have 2 computers on a network that are practically side by side and plenty of open slots in the hub/switch but I do not want to run another cable nor buy the little adapters that say they will do it. HELP PLEASE