Here is a couple of lines to that can be used to clear out the MRU list in Visual Studio. I create many demo projects and prototypes that I like from time to time to clear the list. In researching how to do this it has given me some more ideas in automation to clean my system. The way that PowerShell uses the registry is pretty cool. It basically treats it like a folder structure.
remove-itemproperty . -Name “File*”
The key to this is to browser to the registry directory, then remove any entry that starts with File (note the wildcard). Visual Studio stores each item in the MRU List as a separate entry.