Is there a way to restrict the rendering of a WMSLayer to a specified extent without restricting map panning and zooming? That is, I need the client to be able to pan outside the limits of the WMSLayer, in which case only the basemap should be displayed.

The WMS Server is external and outside of my control.

One idea would be to use a server proxy to receive the WMS request and forward it to the WMS server only if the BBOX is valid, but I would rather find a client-side solution.