You could set MyMode for Spot focus or Spot with Shadow Priority (and maybe add 1/2 stop EV) and have MyMode enabled with the Fn key. Then all you'd need to do is press and hold the Fn key when you need to shoot in the shady/backlight condition. All of your MyMode settings would be enabled once you press and hold the Fn key. See pages 73 and 104 for the functions that can be set in MyMode 1 and 2.
Hey, I may try this myself.
As mentioned above, some fill flash would be a quick method as well.