It's not what you're asking for because it involves the spacebar but this script (which I found in this forum) works pretty well for me:

Space=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; }

Put the mouse pointer over the view you want and press the spacebar. Press the spacebar again and you're back in split view.