Step 1) Go into the S Voice settings and uncheck the Launch SVoice box. This will keep S Voice from launching when you double tap the home button.
Step 2) Install Home2 Shortcut from the Play Store
Step 3) Open Home2 Shortcut and configure it to launch the app of your choosing with a double tap of the home button. The app is pretty self explanatory and setting it up will be pretty straight forward. NOTE: When you get to the end, after you tap "close" it will ask you to set as default. Select Home2Launcher as the default.
Hope this helps anyone who didn't know how to do this. I am currently running CM10, and am using this to launch Google Now with a double tap of the home button.