Using BindAttribute Prefix Directly on Model Class

You could write a custom model binder for the corresponding view model:

public class MyViewModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        bindingContext.ModelName = "some_prefix";
        return base.BindModel(controllerContext, bindingContext);
    }
}

which you could register in your Application_Start and associate with your view model:

ModelBinders.Binders.Add(typeof(MyViewModel), new MyViewModelBinder());

In this example, I have hardcoded the prefix, but you could make the model binder a bit more generic and reusable and take into account the BindAttribute that you could use to decorate your view model with:

public class MyViewModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        // TODO: cache the result of this LINQ query to 
        // avoid using reflecting on each request. After all
        // the metadata of the view model won't change at runtime
        var bindAttribute = bindingContext
            .ModelType
            .GetCustomAttributes(typeof(BindAttribute), true)
            .OfType<BindAttribute>()
            .FirstOrDefault();

        bindingContext.ModelName = bindAttribute != null ? bindAttribute.Prefix : null;
        return base.BindModel(controllerContext, bindingContext);
    }
}

and then all that's left is to decorate your view model with the Bind attribute:

[Bind(Prefix = "some_prefix")]
public class MyViewModel
{
    public string Foo { get; set; }
    public string Bar { get; set; }
}

and request the action that is taking this view model:

/someaction?some_prefix.foo=the_foo_value&some_prefix.bar=the_bar_value