I use shortcuts in %appdata%\Roaming\Microsoft\Windows\SendTo, e.g.
Code:
_calibre books.lnk has target "C:\Program Files\Calibre2\calibre.exe" --with-library "D:\Calibre\Libraries\Books"
_calibre periodicals.lnk has target "C:\Program Files\Calibre2\calibre.exe" --with-library "D:\Calibre\Libraries\Periodicals"
BR