Comair does have a few CRJs which are configured with 40 seats, although I heard a rumor that these are being converted to 50 seat aircraft. Comair is not CASS, but will take as many jumpseats as can fit in back.
Comair has plenty of CRJs that are 40 seats. They are the 50 seat airframe configured with 40 seats.. They've had them a long time and are nothing new.
You'll find the 40 seaters going to JFK, BOS, and DCA quite a bit. As I said, the RDU-JFK runs are 40 seaters and are generally full. Comair runs 3 flights a day on that route. One leaves at 11:10, another at 2:40 and the third at 4:40.