First some background. At the end of 2012 we migrated our vs2008 solution to vs2010 but we still target .NET 3.5. (I know nothing but the latest and greatest here!)
I've found that installing the free Visual Studio 2012 Shell (Isolated) installs the WebApplications v11 MSBuild files. Lighter than a full install of Visual Studio 2012 and no licensing concerns.