I was told by a very nice RA not to do this when I knew that I would not make my 6am flight this past Wednesday as it would affect my "confirmed" status on the earlier flight, and that only confirmed pax for same-day travel can standby for free ... I just walked up to the check-in counter at 1pm and they had no problem reinstating my PNR and confirming me on the 2pm. BTW, you cannot use EasyCheckin to standby on a LATER flight.

I would do what the OP said.

Print out the BP online 24 hours prior so her BF, OOOPS - I mean his BF (corrected on 07/11/05 @ 5:35 pm) , can clear TSA if he needs to bypass long check-in lines and go straight to any GA or CSA or RCC to be added to the DM for the later flight. Or if he happen to be near an airport the day before his flight, just have them add him to the 5pm flight's DM.

Just telll them that he may have to miss his earlier confirmed flight but he is not sure, and would rather protect his place on the 5pm DM.