I found yet another alternative way to save user information (not only IP but also other essential details). It's core-destructive but easy to do if you remember to put the change in your custom-changes.txt file ;):
------------
1. Create a text file (could be named: reg-data.txt or something more unique), place it in main forum folder, and make sure it's good for writing (777).
2. Open: bb_func_regusr.php file and paste the following code ABOVE this:
/* Auto Sign-in */
if(!isset($closeRegister) or $closeRegister==0){
# custom - save registration date in a file
$File = "reg-data.txt";
$Handle = fopen($File, 'a');
$Data = "ID: {$insres} / Username: {$username} / IP: {$thisIp} / Email: {$user_email}\r\n";
fwrite($Handle, $Data);
fclose($Handle);
# end custom - save registration
---------------
That way you'll have a record of all newly registered users and can easily look it up if needed. You can then give link to the file to your trusted moderators ;).