Using @Html inside shared @helper in App_Code

I am building a very basic MVC3 site while I learn and I am having difficulty with the following declarative Razor html helper.

Inside RMB.cshtml inside App_Code folder:

@helper ReplaceCrLf(string strText)
{
    @Html.Raw(Html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

Inside my index.cshtml view:

@RMB.ReplaceCrLf(Model.Post)

This gives me a null reference exception on Html in the helper, because it doesn't seem to know what it is. I can work around this by passing Html from the view to the helper, but I was wondering if there is another way for my shared html helpers to be able to reference Html without me having to pass it in to ever helper I write?

For completeness, here is the working workaround:

In RMB.cshtml in App_Code

@helper ReplaceCrLf(string strText, System.Web.Mvc.HtmlHelper Html)
{
    @Html.Raw(Html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

In index.cshtml view

@RMB.ReplaceCrLf(Model.Post, Html)