USD agent script before a session starts?

I wish to start the Agent Script before a contact is selected from the quick find search. This so we can make consistent the welcome and pre-validation customer experience.

Problem is the Agent Scripting hosted control cannot be launched until there is an active session.

I've tried creating a dummy session (not in any CRM context) and then opening a new session once the contact is selected, problem is closing the dummy.

I'm trying to fire an action call SessionTabs / CloseSession but it doesn't seem to respect the SessionId parameter I am passing, for the dummy session I wish to close.

Two questions:

1. What might I be doing wrong?

2. What do others do to handle welcome/ pre-validation scripts?

Thanks in advance