I am trying to implement custom 404 error handling for requests to the PageFiles virtual folder. I have updated the location section in web.config to this:

  <location path="PageFiles">
    <system.webServer>
      <httpErrors errorMode="Custom" defaultPath="/App_Error500.htm">
        <remove statusCode="404" subStatusCode="-1" />
        <error statusCode="404" subStatusCode="-1" path="/HttpHandlers/ImageResizingHandler.ashx" responseMode="ExecuteURL" />
      </httpErrors>
      <handlers>
        <add name="webresources" path="WebResource.axd" verb="GET" type="System.Web.Handlers.AssemblyResourceLoader" />
        <add name="wildcard" path="*" verb="*" type="EPiServer.Web.StaticFileHandler, EPiServer" />    
      </handlers>
    </system.webServer>
    <staticFile expirationTime="-1.0:0:0" />
  </location>

Now, when I make a request for a file that does not exists in /PageFiles/ I get the following error:

I have unlocked the appropriate sections in applicationHost.config to allow me to override custom errors, however I am not sure what I need to unlock to resolve the lock violation caused by the wildcard handler (EPiServer.Web.StaticFileHandler).

Any info on getting this working would be most welcome, thanks.