I've tried to do this, both as 1K and 1P, and was given no option but to pay the change fee.
Still cheaper than another night's hotel room and meals plus taxi fare back and forth (assuming you do the asking at the airport).
Edited to add that in both cases, I was attempting to stand-by for a flight less than 12 hours earlier than my ticketed flight, but alas, not on the same date.