Have you tried this ruler or know anyone that has?
http://www.fatquartershop.com/bloc-l...trip-set-ruler
It is pricey but if it works properly could be really helpful for 4 patches and 9 patches even. I have many 4 patches in my future with the next few quilts I want to make and this would really help--if it works well.
I have the HST Bloc Loc rulers and they are fantastic.