Use MatchPattern property of FindMatchingFiles workflow activity

I'm customizing the default workflow of build process template using TFS 2010 Team Build. There is an activity named FindMatchingFiles allows to search for specific files with a pattern defined in MatchPattern property. It works if I only specify one file extension. Example:

String.Format("{0}\\**\\\*.msi", SourcesDirectory)

But I would like to include *.exe as well. Trying following pattern but it doesn't work:

String.Format("{0}\\**\\\*.(msi|exe)", SourcesDirectory)

Anyone could show me how to correct it?