Clip external image service in ArcGIS Silverlight Viewer

I have an ArcGIS Silverlight 3.2 viewer and I'm adding an external image service as a layer to the Map Contents. The image service is at:

<pre>http://ift.tt/1z7bykT;

The images cover the whole of a country (South Africa), but to improve performance I would like to access only a small part of the images.

Is it possible to in effect change the extent of the image service on the client side by giving it a new extent?

Thanks