There are no pre written post processing out of the box as it depends on the problem (function set of GP). I will give a short background which you may find useful for what you are doing.

 For generating automated Rules to discriminate certain patterns, i had my GP have basic terminals and non-terminals required for the Rule. I would collect my "exceptional" Rules as a memory pad outside of evolutionary runs, everytime i see some well performing ones. Finally i get a Rule set and wrote my Custom "interpreter" that can parse the GP Individuals as s-expression to evaluate. So ECJ gives you GP and Evolution for free, you need to write custom functions and interpreter for them.

Hope that helps

Uday