How to have the debugger step into the code of another IDEA project

I have a repository that consists of several IDEA projects.

One project creates a jar file which is used by several others.

I need to be able to run the debugger and step into the code of a jar file which is created in an IDEA project from a different IDEA project.

Combining projects is out of the question.  Creating a temporary project consiting of both is also out of the question.

A similar thread from 2009 is at http://devnet.jetbrains.com/message/5252897#5252897, Re: Two Projects - One Tomcat - One debugger?

I hope in the years since then this has been made easy but I can not find any documentation on how to do it.

Note: I am not using maven