What is the best way to convince the doc to prescribe a constant script of percocets?

please no lectures or drugs are bad crap.i really have bad knees but i am fully aware that these are hard as hell to get prescribed do to the fact every one wants them...the doc always tells me to take advil,aspirin some times gives me vicodin and a sure every one is aware that none of those really work. ps knees are messed up due to skateboarding when i was younger. :(