If you haven't already done so, gain an extra key and open up your System Preferences > Keyboard > Modifier Keys ... and rebind CAPSLOCK to No Action.
- Install PCKeyboardHack
- Open System Preferences > PCKeyboardHack
- Change "Caps Lock" to keycode
Open System Preferences > KeyRemap4MackBook > Misc & Uninstall
- Click "Open private.xml"
- Copy and Paste the private.xml provided with in this gist.
- Open System Preferences > KeyRemap4MackBook > Change Key
- Click "ReloadXML"
- Toggle open "TMUX Key Remappings"
- Check "TMUX: Right Control to Control+B