4 hrs searching has only yielded this 
http://i1121.photobucket.com/albums/l512/nimetanu/ExternalMacbooktrackpad.jpg 
so what i'm proposing is very possible. A smaller older model mac track pad with the controller built into the track pad could function nicely. 
I remember a blog about eepc modifications basically cramming extra components into a tiny space. 
I smell a project