Geoff, you don't mention anything about your PC friends monitor resolution.
I run Lightroom on Mac and PC. The Apple cinema display is 168'px wide and the panels largest size brings it to just under the "y" of Library.
Its smallest size which makes them about 37' and 245 pixels respectively.
On my PC (which is a laptop) the resolution is 1'24px. The panels are 388 and 25' respectively. Not counting any borders or scroll areas.
Now in my opinion the PC with its resolution so low display panels that are way too big at their smallest size.
It would seem to me that the limitation on the panels size is a pixel amount rather than a percentage amount of working area so the larger the display are the smaller they will appear.
So the question remains. What is the resolution of your friends monitor. If it cannot be increased beyond 12'' then he'll want to get used to the hide shortcuts.