So here's my final solution:

1. I created 2 scripts files called viewfloor1.scr and viewfloor2.scr in the same folder as the map. Of the general form:
HIDESHT 1 FLOORS
SHOWSHT 2 FLOORS

2. I went to [Tools>Macros>Make Hotspot] and entered something like:
scriptm $viewfloor2.scr;
and selected the rectangle for the hotspot

3. Now I can just click on a hotspot and it shows the appropriate floor. Very slick.

Thanks for the help everyone.

Mike