StuKirby,
This is hypothetical but not tested as my own lab is unavailable for maintenance. In
Security ›› Application Security : Sessions and Logins : Session Tracking
you can enable Session Awareness, perhaps select None for Application Username and then if you see under Block All section you can enable an IP Address threshold (and above that amend the Violation Detection Period). Alternatively Delay Blocking allows a number of violations and then blocks. You would need to enable the following violation to
Block Access from disallowed User/Session/IP
Does this help achieve what you need to achieve?
N