Add property to dynamic object .NET

I probably want too much, but my scenario is

public dynamic CreateConfigObject(JobConfigurationModel config) {
    dynamic configObject = new { };

    configObject.Git = new GitCheckout {
        Repository = config.Github.Url
    };

    return configObject;
}

Of course, it fails on configObject.Git since this property does not exist. I want to be able to add any number of properties at run time, with out any beforehand knowledge of number and names of properties;

Is such case possible in C# at all, or my ill JavaScript imagination starts to hurt me? :)