This sounds like a 'Poster' feature which SMF doesn't support at the moment. However, you could implement this feature in your application by extending from the player. The steps are (roughly) as follows:
*Extend from the Player
*In the template XAML for your player add a UI element to display your custom content (Image, ContentControl, etc).
*In your custom Player display your content when it loads.
*Hook into the mediaElement.CurrentPlaybackStateChanged event and look for mediaElement.CurrentPlaybackState == PlaybackState and hide your custom content.