The trick is to (with the windows up) move your head as far as you can to the left and then adjust the left mirror so you can just barely see down the side of the car in the right edge of the mirror. Next with the seat belt locked or at least without moving your butt out of the seat lean to the right about the same amount and then adjust the right mirror so you can just see the edge of the car in the left edge of the mirror.

This should allow you to see objects just starting to move off of your center mirror slide into either side.

Hope that helps. Cheers!