Unfortunatelly there is no portable way of doing this in general. I suggest that you open an issue with the hibernate validator team and request that they provide an option (e.g. a system property) to suppress the extension.
I'm currently looking at the org.jboss.weld.environment.se.Weld
What if Jozef we could add an hook to the Bootstrap::loadExtensions method and then provide a way to skip unwanted extension ?
Would that do the trick ? What do you think of that ?