You have a meeting in my home town! There is a way to do this it is by purchasing two one way tix. I.E. PHX-IAD-RIC (make sure you do not check luggage) get off at IAD. Then since you aren't on a rt ticket and have seperate pnr's your second one way RIC-IAD-Phx won't get cancelled.

I put in a sample date of 10/19 phx to IAD and they routed through los angelos at a cost of 290 out bound and 276 on the return.

Also there is risk in doing this if everything goes haywire they will want to put you through houston or cleveland to richmond. Also if you did 2 one way tix you could do PHX-IAD-RIC on the outbound and IAD-PHX on the return, so you wouldn't have to drive to richmond.

Also a Manassas to Richmond drive sounds about as pleasant to me as a root canal and can take 3+ in rush hour traffic.