this is supposed to be true and usually is, but there are noted exceptions in the upgrades thread that do occur. they are due to a computer bug and it isnt supposed to happen that way. continue to watch the flight for any last moment cancellations of booked seats up front, and if you see one, run a dummy booking to check to see if U is open...if it is, you can sometimes sneak one through the 5-hole by re-running online check in on your reservation and get an offer for a paid upgrade. note if only one seat opens you'd have to split the reservation to get it.

best of luck for a speedy recovery for your son.