On the way to WP8.1 CustomMapTileDataSource

gistfile1.cs

                var im = new byte[100]; 
                var ms = new MemoryStream(im);
                var rs = RandomAccessStreamReference.CreateFromStream(ms.AsRandomAccessStream());
                
                // http://msdn.microsoft.com/en-us/library/windowsphone/develop/windows.ui.xaml.controls.maps.custommaptiledatasource.aspx