Hi Aerial,
Sorry, I had the threads wrong in my first reply. The correct answer is that it is indeed possible to create the setup you want by cascading KVM switches. A detailed description is in the handbook for the S4-0812 series of KVM switches, which can be found here:
http://manuals.ts.fujitsu.com/file/10410/kvm-s4-08... Please see chapter 2.4 for detailed advice, diagrams, and tables.
With best regards