You certainly can do this.
I myself have done this exact flight.
Comair is a franchise carrier of BA thus allowing travel on a Xone. Other carriers include BMED, BA CitiExpress, Sun-Air, Loganair and GB Airways.
There is no First Class on this route so you will be slumming it in Business Class.
Have a look here and click on Planning an Explorer Trip, about affiliates and which other franchise carriers you can use.
This thread also has alot of information regarding XoneX. It also answers your question about BA metal flights.