How can I load external layout files using RazorEngine?

I've been trying for days (really, days) to use "external" files (provided from a different server using an ashx handler) as layouts in Razor.

@{
    Layou开发者_如何学Ct = "http://someServer/templates.ashx?path=/my/template.cshtml";
}

This gives me an error about the path having to be a virtual one.

I've tried everything I could think of: VirtualPathProviders, custom RazorViewEngines, etc.

Nothing helps, has anyone done this or can someone give me a hint?

Make a VirtualPathProvider that handles virtual paths that start with a magic token and passes all other paths to its Previous property.
For example:

public override VirtualFile GetFile(string virtualPath) {
    if (virtualPath.StartsWith("~/MySpecialTemplateServer"))
        return new MyServerVirtualFile(virtualPath);
    else
        return Previous.GetFile(virtualPath);
}