[Dovecot] Variable similar to %u but providing the username changed by a database lookup?

Hello,

Variable %u may be used in dovecot.conf whenever the "full username" is needed.

But the expansion of %u returns the username before a possible change performed thru a password or user database lookup (e.g., in the case of a SQL database, thru as "AS user" clause).

Is there a variable that would expand to the changed name when used in the configuration file?

TIA, Axel