How to use the new VS 2010 configuration transforms and apply them to other .config files?

I have setup some configuration transforms in my web.config for my connectionStrings, etc. But I have separated out some areas of my web.config into separate files, ex) appSettings.config.

How can I configure Visual Studio and MSBuild to perform config transformations on these additional config files?

I have already followed the approach of the web.config to relate the files together within my web application project file, but transformations are not automatically applied.

<ItemGroup>
    <Content Include="appSettings.Debug.config">
        <DependentUpon>appSettings.config</DependentUpon>
    </Content>
</ItemGroup>