EJB3 interceptors do not run on method calls to "this". Only on calls from another object.
What I can do for you is promote the BusinessProcessInterceptor.createProcess() method to a public API, so you can call it directly.
Add a feature request to JIRA.
Anyway I am going ahead with another seam component ProcessInitiator with the target seam component injected (one which has process1, process2 etc).
So, I got a little facade which enhanced the design.