How to debug GWT project server side code using GPE(server code been packaged as a jar)

[July]

Hello:

 I have a GWT application which i can debug the server side using GPE easy when the server and client located at same project, now i remove server side code and package it as jar, add it as project dependency, Seem there is no way to debug server side code anymore, Any ideas? By the way i'm using Maven to organize my project. Thanks