On a train presently, only equipped with my mobile.
The fare code of my ticket is INNN3C, covering travel ALG-JFK. For my plans, the possibility to make a longer stopover in LAX was useful, especially when no minimum stay in JFK was required. The Premium Fare Deals thread, which I linked to in my previous post, have only elaborated on the west coast hub routing one way or both, IIRC.
Adding BWI, with necessitating another transfer, like CLT, into some quick searches increased the price from +55% to +350%. If BWI is a must, there must be some limitation I can't see on the mobile, that drags the price up. Without JFK, this fare does not seem to work.
Good luck in circumventing the obstacles, or maybe compromise and have a ticket to JFK (by all means, don't miss the turn-around in LAX, with/without stopover) and buy a separate ticket JFK-DCA r/t + shuttle to BWI, train NYC-WAS or a rented car JFK-BWI.