How can I render the result of Html.Action() from within a custom helper?

Due to an implementation detail, I have what would be a partial view that needs to be a full-fledged view "rendered" using <%= Html.Action(Model.ViewerToRender) %>. It works fine in my dev spike where I can put that line directly on the page, but in the production code it must be in a View开发者_如何学CPage helper method that returns a void. Given the htmlString variable in the following code, how can I render it to the page from within this helper?

public static void RenderDocumentViewer(this ViewPage<DocumentViewModel> page)
{
    if(!page.Model.UseRenderPartial)
    {
        var htmlString = page.Html.Action(page.Model.ViewerToRender);
        // The following line is what I don't know how to do:
        page.RenderHtml(htmlString);
        return;
    }

    page.Html.RenderPartial(page.Model.ViewerToRender);
}

Try

page.Response.Write(htmlString);