We like to use the Alamo at the Dolphin, too. I often will walk or boat to the Dolphin after spending a morning at Epcot or HS. I think they may be able to pick you up in a shuttle at your resort, as well, but I am not sure of that.
The reservation desk is only open until 4PM, so if you need to pick up later than that, I don't think there is a way to use that location. You can drop the car off before they open, as the Dolphin valet parking attendants can process that return.