Upgrading / uninstalling SQL 2008r2

This has happened to me before - sometimes when you want to un-install SQL 2008 (including r2) to clean-up before upgrading or re-installing you get an error message saying something like

Warning 26003. Microsoft SQL Server 2008 R2 Setup
Support Files cannot be uninstalled because the
following products are installed:
SQL Server 2008 R2 Common Files
Microsoft SQL Server 2008 R2 RsFx Driver

 
But these items do not appear in the Control Panel | Add/Remove programs applet. So how do you uninstall them?
 
Here's how:
http://myitforum.com/cs2/blogs/jnelson/archive/2011/08/30/159139.aspx