How to add extra namespaces to Razor pages instead of @using declaration?

Is there some sort of magic I need to use to get the namespaces in the pages/namespaces element in the webconfig?

<pages>
    <namespaces>
        <add namespace="System.Web.Mvc"/>
        <add namespace="System.Web.Mvc.Ajax"/>
        <add namespace="System.Web.Mvc.Html"/>
        <add namespace="System.Web.Routing"/>
        <add namespace="System.Web.WebPages"/>
        <add namespace="System.Web.Helpers"/>
        <add namespace="MyCustomHelpers"/>
    </namespaces>
</pages>

The above just doesn't want to work. I know the namespace is fine because when I put the @using MyCustomHelpers at the top of the page it magically works.

This is so that I can get the Html.SomeFunction() to work without having to put @using at the top of all my pages