Route changers are always level 2 power plays and those take time to build up. So a quick way to do it is just put yourself in 8th at the start of a race and get draft from everyone else. This should build up the meter quickly. Don't use power plays unless there's a shortcut or unless you know you can get it back quick enough. Since some stages don't have route changer, I suggest Airprort Terminal because I know it has three route changers.
EDIT: 1st is the tower that falls and puts you on the tarmac. 2nd is after the finish line which takes you underground. 3rd is after the finish line as well but this one takes you around the airport, through the shuttle area, and puts you back on the tarmac.