In regards to the original question, not the BB-related issue, I think I use the solution you’re after. I wanted to be able to redirect to a page based on the user’s login name, not the displayed username.
I had to edit the plugin, though.
Edit the file sidebar-login/includes/class-sidebar-login-widget.php.
You need to change the first part of the replace_tags() function:
public function replace_tags( $text ) {
if ( $this->user ) {
$text = str_replace(
array( '%username%', '%userid%', '%userlogin%' ),
array( ucwords( $this->user->display_name ), $this->user->ID, $this->user->user_login ),
$text
);
}
And then use the %userlogin% tag in your widget.
Hope this helps someone!