Gordon Edes has some interesting mixed reporting and speculation related to both Morse and ALR. If the Napoli deal falls apart (the focus of the link), we've all thought Boston would then look at ALR. however, Boston has also been very careful not to give up a draft choice, give up high quality prospects in trade, or bind themselves to longer term contracts that could block players. Were the Napoli deal to fall apart, Edes suggests the Red Sox may be more interested in Morse than ALR.
Napoli was projected to fill Boston's void at first base. If the deal doesn't come through, the Sox could turn to free agents Adam LaRoche or Nick Swisher, although both would cost the Sox a draft pick as compensation. They could also wait to see if Washington signs LaRoche, which could make the Nationals amenable to moving outfielder/first baseman Michael Morse in a deal.
[note - this was before the Swisher signing by the Indians]
I've mentioned the surplus of lefty relievers they have - Miller, Breslow, and Franklin Morales - as part of a 10 pitchers into 7 slots bullpen. I could easily see Morales for Morse after ALR signs with the Nats.