Copy jad.idekeybindings into ~/Library/Developer/Xcode/UserData/KeyBindings/, creating directories as necessary. Or clone the repo directly into this directory:

$ cd ~/Library/Developer/Xcode/UserData/
$ git clone git@github.com:jad/xcode4-key-bindings.git KeyBindings

To see an example of implementing multi-action key bindings look at IDETextKeyBindingsSet.plist.

To use these bindings copy IDETextKeyBindingsSet.plist into /Developer/Library/PrivateFrameworks/IDEKit.framework/Resources/ then open Xcode's Key Bindings preferences and assign a key combination to them.