How can I have two content areas on a single page?

I have this WordPress site I’m currently working on for a client. The problem is that the clients wants the information on their sidebar to be different for every page. So obviously I’m not going to create a separate sidebar for each page.

Ideally, what I would like to do, is have an extra textarea on the content edit page that would allow them to put in the content for that page’s sidebar.

Does anyone know of a function or a plugin that would allow me to do this?