Reading Mac OS X Hints I learned about BetterTouchTool, which allows rebinding the four finger swipes. The process is a little bit tricky, but here is how I managed to do it:
- Disable four finger swipe left/right.
- Disable any associated hot keys to the exposé actions or dashboard invokation from the system preferences menu, keyboard, shortcuts.
- Run BetterTouchTool (I'm using 0.306). It will append itself to the menu bar with many other icons on the top right of your screen.
- Click on the icon on the menu bar and choose preferences.
- Create a new binding for four finger swipe left, and bind it to a shortcut combo you would never ever use. I'm using Ctrl+Alt+F12, and since that key is hardwired to volume up, I have to press Fn+Ctrl+Alt+F12. Pretty elaborate.
- Create a new binding for four finger swipe right, bind it to shortcut (Fn+)Ctrl+Alt+F11.
- You can close now the preferences window and return to the shortcut window from the system preferences.
- Select the Dashboard and dock section, activate Dashboard and write as keyboard shortcut (Fn+)Ctrl+Alt+F12.
- Select Explosé and Spaces, activate Windows of the application and write as keyboard shortcut (Fn+)Ctrl+Alt+F11.
If everything has been done correctly, you should have now four finger swipe left bring up or close the dashboard, and four finger swipe right activate explosé only for the active application.
As a special treat, the four finger swipe can also be customized inside specific applications. For instance, in Safari I've made the four finger swipe change active tab to the left/right.