Figured it out (nearly). There is a function called EditorView in WinIE.js. I can call this function from the Editor Page using the On Click Event of a button (JavaScript) as below

 

onclick="EditorView(Editor1.0)"

 

Where:
0 = Normal View

1 = HTML

2 = Preview

 

This allows me to set the view of the page as desired. Just need to get this working now from VBScript