Ability to mix JNDI injection vs manual creation of objects

Assuming we get this notion of NoSQL datasource in WildFly.
Depending where the code is run, we want the connection pool (`MongoClient`) to be retrieved from JNDI or built by this extension.
How would that kind of magic happen? I imagine `PersistenceContext` has something like that (or should :) ) to help the mix of unit tests and actual deployments.
