Or you can create a seperat account on your computer and use that for just the basegame. You can have a bunch of accounts on one computer.
The only way this could work is if you install the base game in another folder other than the default. Just thinking it through, I'm still not certain it would work because the registry settings are still set. This could either a) prevent the second installation, b) force use of the previous installation, or c) break the current installation. Basegame starter changes the registry settings behind the scenes prior to running the version of the game you want. Some people have had problems with it, others, to include myself, have used it without any consequences.