Does anyone know how I can get the normal ringer to ring when I have the ear-piece plugged in?

I want the normal ringer to ring, IN ADDITION, to the ear-piece ringer.

I prefer to talk through ear-piece but it is not comfortable in my ear for a long time so often leave leave my ear-piece plugged in to the Treo lying on my desk. I now miss a few calls because I don't hear it.

Any ideas? Thanks