Only by walking around to their desk I'm afraid. otherwise you can kill the connection remotely, but I wouldn't think that were safe to do.
I believe there is some code floating around somewhere that will allow you to read the ldb file to find out who is logged on and send them a network popup asking them to log off.
I think the best thing is just to email the users asking them to log off.
Updates should not be done on the live version. One of the main reasons for having a frontend is so you can make amendments to a copy and simply replace the existing frontend with the copy.
I'll try to find that code for reading the ldb
Mary