The simple answer is that you can't.
I've just run into this issue myself. It strikes me that requiring an additional client license, and a full VS install simply to_build_a project is way over-the-top. The TFS alternative is obviously better (it being a server product) - but potentially still requires additional licensing. Anyway with increasing numbers of shops running continuous integration I think it removes a significant amount of desirable functionality from the Visual Studion database project story.
If you want to try and get database projects built only using MSbuild vote here.