Can you post the complete exception stacktrace?
This was already answered on WildFly + java Preferences cannot find custom preferences class in classpath - Stack Overflow. To reiterate while this might be possible it would be a bad idea. No other application, include the any parts of the server, would be able to use the preferences API if you provide the implementation in your deployment.
James R. Perkins
I dont have the complete stack trace anymore.
But it seems to be fixed by migrating the startup service using JMX Service to a @Singleton + @Startup EJB.