How can I debug a Java Google App Engine app while using the GAE Maven plugin?

I have set up my pom.xml like so, and it appears to be working for the most part, I can start the devserver and update the application.

My problem is that I can't seem to debug the devserver.  I tried launching the devserver maven goal in debug mode from within IDEA, but when I set breakpoints they are ignored.

I found in the GAE Maven plugin docs that you can launch the devserver in debug mode with the following configuration in the pom.xml:

    <jvmFlags>

      <jvmFlag>-Xdebug</jvmFlag>

      <jvmFlag>-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmFlag>

    </jvmFlags>

However I don't know how to tell IDEA to connect the debugger when I start the Maven Run/Debug configuration.

Can anyone point me in the right direction?