There is a tutorial by tweezit that shows how easy it is to enable this effect - but it requires you to change framework-res.apk. There are different threads that offer those modified files, but to combine different modifications, there have to be many different files with all possible combinations.
To avoid this, I'm developing the Xposed framework, which allows such modifications without changing any APK (or JAR in this case). All you need to do is install the Xposed framework app (root required) and then the attached module for it - both with the normal APK installer as any other app.
Tested with Stock LPQ, but should work for most ICS ROMs (not sure about CM9 though).
This mod is no longer supported. Please use my Tweakbox instead.