I opted out with no issues in DEN in May. Got the random beep at SFO Terminal 4 yesterday and was already saying opt out when I realized there were no rapiscanners nearby for the Pre line. They did a very perfunctory pat down, not like when I opted out in the International Terminal without pre at the start of my trip.
If your brother isn't comfortable or pressed for time, just ask for two comment cards after clearing the screening. Fill it out and drop one there in the box and mail the other to the address on the card.