You can standby at some alternate airports:

C. SAME DAY STANDBY-UA PASSENGERS HOLDING CONFIRMED RESERVATIONSAND TICKETS MAY STANDBY FOR EARLIER/LATER SAMEDAY FLIGHTS BETWEEN TICKETED CITY PAIRS AT NOADDITIONAL COST. IN ADDITION TO THE ORIGINALAIRPORT OF DEPARTURE/ARRIVAL PASSENGERS MAYCHECK IN AND STANDBY TO/FROM AIRPORTS LISTEDBELOW UNLESS RESTRICTED BY THE AIRPORTPROVISIONS OF THE FARE
CITY AIRPORT
CHI ORD/MDW
NYC JFK/LGA
WAS DCA/IAD

Thats on a Q fare I am holding. I swear I have seen others with more alternate airports including BWI in the WAS region. I guess you need to look at your fine print...