Probably not the most graceful way to do it, but it works.
my $exp = $c->calculate_initial_session_expires;
$c->_session_expires( $exp );
+ #
+ # since we're setting _session_expires directly, make load_session_expires
+ # actually use that value.
+ #
+ $c->_tried_loading_session_expires(1);
$c->_extended_session_expires( $exp );
$exp;
}