Hi John, there isn't a way to do it on middle click but you can assign this script to the space bar:

script:if ( moi.ui.mainWindow.viewpanel.mode != 'split' ) { moi.ui.mainWindow.viewpanel.mode = 'split' } else { var viewport = moi.ui.getViewportUnderMouse(); if ( viewport ) { viewport.viewPanel.mode = viewport.name } }

Then when you push Space it will switch either to the view the mouse is over if you are in split view, or back to split view if there is one view maximized.

That one is listed in the shortcuts section of the help file here:
http://moi3d.com/3.0/docs/moi_command_reference11.htm#shortcutkeys

There are some other various view scripts listed here:
http://kyticka.webzdarma.cz/3d/moi/

These are linked to from the Resources page: http://moi3d.com/wiki/Resources

- Michael