We're flying IAH-ORD-LGA later this week on AA... There are two earlier flights from ORD-LGA that we could make with connection time. We'd like to stand by for an earlier flight for the second leg. Can we get on the stand-by list for earlier ORD-LGA segment when get to IAH? Is it possible to get on the stand-by list earlier by calling reservations? We're not planning to check luggage, in case that matters. (FWIW,currently tickets on the earlier segments are 1/3 the price of ours, indicating they have more availability than ours.)