IIS 7.0 Custom Error page for error code with a substatus

Has anybody successfully created a Custom error page using:

1. The IIS 7.0 GUI
2. a substatus error code (e.g. 404.13).
3. using "Execute a Url on this site" (as opposed to the static File or Redirect options)
4. an .asp error page

The only ways I have been able to get my application, which is a legacy classic .asp app, to display a custom 404.13 error message is to either use the redirect option with a static file (.htm) or use the static file option with an htm file from the file system.

Secondary questions:

Is there some restriction is IIS 7 to custom error pages for substatus error codes?

Also, is it ever recommended to return a substatus code because of security concerns?

In the <httpErrors> element of <system.webServer> you can specify a subStatusCode attribute: http://www.iis.net/ConfigReference/system.webServer/httpErrors/error

However the ASP.NET configuration elements (children of <system.web> do not support sub-status codes.