Ignore ghost client rule??

In our Hobbit 4.2.3 Server, I have a ghost client and don't know, what machine it is. The client is connected via DSL and hasn't a fixed IP. It must be a notebook of a coworker, I think. Anyway.... Is it possible to hide those ghost clients?

I'd like to not see it anymore in the ghost client list. Is there any way to do it?