Richard,
I get what you mean.
Using your Wetlands Tour as a sample (
http://multimediaaction.com/wetlands/wetlands.html)... You'd like to setup a your "controls" (bottom left of the sample) as a single jpg (or png)... like this...
(or something similar).
Then, place "hotspots" on top of the control image.
Is that right so far?
If so, then you CAN do this with plugins.
If your control "buttons" in the image are more or less square, then you could use a transparent 1x1px *.png as the plugin that sits over the control image button and receives the onclick event (or onhover, or on... whatever).
If you need a transparent png... I'll try to add one later... I'm getting server issues everytime I try to do something now.
OK - it's working again...
Here's the 1x1 transparent png...

hmmmm... it really is there... I figured it would act like the other attachment above and make it "visible" in some format.
I've emailed it to you as well.
When you add it as a plugin, just position it as needed with x and y and set the width / height as needed to cover the area you want.
If you don't set the transparent overlay as a child to the control menu image... then you'll want to make sure to set the zorder's correct...
control_menu - zorder=1
overlay - zorder=2
Hopefully this will help.... feel free to come out from under the rock and ask for additional clarification.