Test 1: Failure
Test 2: Partial Success (Split 1 mouse into 2 machines)
Test 3: Pending

So, the short answer is the hub solution won't work. I guess the P2P connection does happen for each mouse to each PC. So after testing different ideas, I came up with a way to build this. I had a couple spare crappy wireless mice sitting around that I wasn't going to use. I ripped them apart and soldered the DATA+ and DATA- from a bare USB extender to both mice and plugged them into my machines. The PCs detected the mice and when I moved the primary (3rd) mouse, it worked! The best part was that machine A and machine B were at different resolutions and the mouse movement scaled correctly!

I need to tweak some things and then figure out how to do the same thing on a keyboard. I'm sure I can score 4-5 crappy keyboards for free. The hub idea was a failure, but I did manage to find a cheap way to multiplex mice. I'll submit my project log next week sometime.