Short answer: you can't. Use MSIEXEC /x
Long answer: When you run the MSI file directly at the command line, all that's happening is that it runs MSIEXEC for you. This association is stored in the registry. You can see a list of associations by (in Windows Explorer) going to Tools / Folder Options / File Types.
For example, you can run a .DOC file from the command line, and WordPad or WinWord will open it for you.
If you look in the registry under
HKEY_CLASSES_ROOT\.msi, you'll see that .MSI files are associated with the ProgID "Msi.Package". If you look in
HKEY_CLASSES_ROOT\Msi.Package\shell\Open\command, you'll see the command line that Windows actually uses when you "run" a .MSI file.