Yes, it's possible to have it, but you need to be experienced user to implement this. Your case is very custom, and I can give you only general advices.
Pay attention to bb_cookie.php file, it has all functions to manipulate with user login information. You may include the file in your script, but keep in mind the full path to the script.
The most important function is user_logged_in() which generates $user_id (if $user_id=0 this means user is not logged in). Call this function to know user's ID, and display login information correspondingly (you can use the same routine and templates even, as miniBB uses).
Your cookie settings should be set and work on the whole domain.
$cookiepath='/'; //this is a must