Just open sourced this today... Hope someone finds it useful.
https://github.com/Venditan/appengine-deploy
What is this? Is it different from appcfg.py?
This allows you to deploy the same code/application to multiple target environments (local, multiple different App Engine projects).
Critically, it also allows you to manage environment variables distinctly for each deployment target.
This tool uses appcfg.py to actually push the deployments out, but it builds a dynamic command, overriding the target application id and environment variables at deploy time.