I read on MSDN Forums that it is not possible to use other configuration than Release and Debug. This is wrong.
I am using it for Tech Head Brothers Portal, what you have to take care of is how you set your configuration. On the following picture you see how I defined a new Staging configuration and set the Web Deployment Project WebApplication.csproj_deploy to build using this configuration.
Then you are able to use it this way in your MSBuild:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Staging|AnyCPU' ">