No, I believe this is not possible. That's indeed the fundamental difference between a Named User CAL and a session CAL (the QV wording for concurrent license). A Named User CAL is bound to a named, identified User.
Or from the QV license documentation:
A Named User CAL (an identified user on a server) has access based on user identity and is valid for all documents on the server, therefore any number of concurrent sessions from one user on one machine at any time is allowed.
This license allows one user on one computer to access QlikView documents. This means any number of
concurrent sessions from one user on one machine with the same client (e.g. AJAX, IE Plugin, etc) at a time is
allowed. Anonymous users are allowed, no identification of the client users is necessary. Minimum Session
time is set to 15 minutes.
You can change or delete / reassign the named user of a Named User CAL manually though. But that's more kind of user maintenance than a concurrency thing.