Hi David,
This is one of the few options listed in the Install Guide that we removed from the admin console interface to allow the App Volumes team time to design a better way to implement this feature in the new application package framework. In the interim, the function still exists in App Volumes 4 manager console under the VOLUMES (2.X) section, and you can still use the function with your 2.18 agents.
We look forward to bringing back a better design of this immediate attach feature as part of a future release.
Thank you for your understanding.