Here is the how to:
1. Press [Windows]+[R]. A "Run" dialog should appear.
2. Now type in "notepad %programfiles%\Microsoft XDE\1.0\WM7_Skin.xml"
and replace onClick="0x3B"
so it would look like this:
4. Now start your emulator and press and hold the back button
I have found a way to enable quick app switching (or what ever it is called) in the Mango emulator. It seems to be a little bit buggy but it works. Here is a screenshot: