There isn't any mechanism to inject a custom state transfer integrator/generator at the moment - and won't be for the foreseeable future.
Why do you feel the default notification when state is integrated is insuffcient?
Because it is not possible to keep external resources in sync with the cache.
If a cache contains node A before the transfer, and node A is recreated by the integrator (e.g. network interrupt), no create notification should take place. Likewise, when data is modified (application hook necessary to decide this), node modified events should be fired. Finally, it must be possible to detect removed nodes.
Also, even though delete-all and create-all may work for the cache (although arguably a poor solution), the same cannot be expected from listeners/business semantics.
Fair comment, I see your point. Perhaps what you need to do then is to contrib a patch that does integrate state in such a manner that it records creations, deletions and modifications, and fires off notifications accordingly? :)
Have you created a JIRA feature request for this?