I seem to have it working now.
I was very confused about zone numbering. I've no idea what controls the order of the zones in my MC installation, but it's certainly not in alphabetical order. I was originally following the guidance provided by Glynor (the author of the wsf script) in the thread I linked in my OP, which stated "1:0 corresponds to the first zone, 1:1 to the second, 1:2 to the third and so on and so forth". That does not appear to be correct in my case.
A process of trial and error (greatly assisted by the Overview that appears at the top of the Playing Now section in the MC interface and indicates which zones have a detached display) proved that Zone 0 was my 2nd zone, Zone 2 was my 5th zone, and Zone 3 was my 4th zone. I don't know the meaning of Zone 1, as it simply generated a black rectangle and didn't trigger any detached display indicator in Playing Now: Overview.
I tried to add another command to set Zone 0 as the current zone but mc32.exe /MCC 10011,0 doesn't work. Have I got the syntax wrong for that command?