Wouldn't be possible to implement the following (just my ideea):
1. each unattended host would have a checkbox beside the connection icon for "Accept client connection"
2. each client already has a unique ID, so you could assign the checkbox status to the client's ID and store it in a file (or db in the future).
3. when the client connects to the sever, test if the client is accepted (checkbox on) or not. If in the file the chekbox status is set to on for the connecting client's ID, the client is able to connect to the relay server OR if the checkbox status is set to off then the script/program rejects the client's connection to the relay server. This way the client SC will not be able to connect to the sever.
This is just my ideea. Maybe it's not so good but I wanted to share with you.
Regards,