Incorporating secondary motion to enable changing strings on an upstroke.

DSX Elbow player here practicing the Pepsi Lick in order to develop the habilty to change string on an upstroke with the help of a secondary motion (forearm rotation) with no improvement at all. Decided to open a TC to get some advice on how to aproach the practice of lines with mixed scapes/string skipping. P.D: sorry for the bad english,not my first lenguage.