After a bump on NW, I've had luck getting them to rebook my itinerary partially on another carrier.

So, why not connect to the BOS-AMS or JFK/EWR-AMS flights by flying from DCA on US, DL, or CO? With the last two, particularly, you'd still get miles, and probably a bonus for being rebooked into Y.

That way, you don't have to take the risk of not making it to IAD in time for your flight.