Please, PLEASE take this advice: If you are not 100% familiar with the NEC and residential wiring practices, hire a licensed electrician! Wiring is NOT a HOBBY!! As a licensed home inspector and electrical inspector I have seen hundreds of homes wired with dangerous handy-man wiring, and several instances of past electrical fires! It only takes one mistake and one set of circumstances to cause terrible loss or even death! Clueless, I strongly advise you to invest the $125 or so for a professional to add your extra desired circuit. Gs, no offense, but your description of wiring practices and electrical to me wreaks of handy-man caliber knowledge. You should be careful to whom you give residential electrical installation guidelines to!