The trick here is to rewrite the path once again in the page's Init event. You need to store the original path in a Context.Item so you can retrieve it in the page's init event. Like so:

// Global.asax
Context.Items["originalUrl"] = originalurl;

// Page's Init event
protected override void Page_Init() {
    if (Context.Items["originalUrl"] != null) {
        string originalUrl = Context.Items["originalUrl"];
        Context.RewritePath(originalUrl);
    }
}

What this does, is the page will then load all relevant images, controls etc according to the originally requested path.

I just had the same problem and found a blog somewhere describing the above.

Hope that helps!

Sean