I am happy to announce that there is a new way to configure a ProcessEngine and deploy processes.
You can now use the Process Application API.
Luckily, using this API in your project is quite easy.
There are three things you have to do:

1. provide a processes.xml file
2. make a subclass of org.camunda.bpm.extension.osgi.application.OSGiProcessApplication
3. export it as OSGi service

After that the process will be deployed and the engine will be started and exported.
To show you how easy it can be I created an example project.

Please note that the feature is right now only usable when using Blueprint.
Also you'll have to build camunda-bpm-platform and camunda-bpm-platform-osgi yourself. But the next releases should be right around the corner ;-)

Unfortunately, I wasn't able to activate the process application local scan for process definitions (see here). I couldn't figure out a way to find resources inside an embedded jar.
Neil Bartlett mentioned the BundleWiring class. Seems like I have to wait until we upgrade the project to OSGi 4.3.
If anyone knows a way please let me know.

So, enjoy the OSGiProcessApplication and give me some feedback if you want to!