Thanks a lot guys,
I'll have a go with migrating the project later today... Who knows, if I find a TP with a matching screen resolution (800x600), it just might work.
Now if migrating doesn't work out, I found an ancient Siemens keyboard with a relatively small (4,5x9,0cm) PS/2 driver PCB that I unhooked from the kbd and could mount directly in the PC. So now WinCC no longer makes a fuzz about the missing keyboard!
I know it's a rather silly solution to a problem that shouldn't have existed in the first place, but at least I would get the compact setup I want. It would sure beat the kbd connect/disconnect routine everytime the PC had to be restarted for whatever reason...