Tollerance is a fact of drug-life, if you use daily you're going to go through the roof, so space it out a few days at a time and you can keep yourself in check... also, if you take a slightly-higher-then-normal dose of DXM (yeah, "RoboTrip" aka cough-syrup) can also increase the effects of the drug and help keep tollerance to a minimum, if you're looking to potentiate the effects of the narcotic something like hydroxyzine pamoate ("Vistaril" - a non-controlled prescription drug you could easily get) would do the trick just dandy...
Maybe use once, wait 3-5 days then use again... in other words, keep it to the weekend and you will always get off on those 4 Perc's .. when you move to using from the time you get up until the time you go to sleep, your habbit gets expensive!