Header view in ScrollView (WebView)

I'm would like to put a header in the scrollview, which scrolls with the view.

There is a ContentInset property in UIScrollView (UIWebView) for this, usable from a custom renderer. You can add a subview to the scrollview, position it at top, and set the ContentInset to the height of the header. And eventually override LayoutSubView to reposition the header while scrolling if needed.

But i don't know how to add a view hierarchy created in Xaml to this header in the custom renderer. Any idea ?