Ticketing-counter agents CAN put you on the SB list- but be careful, though- sometimes when I'd wanted to get onto the SB list ASAP (expected to be full, etc.) if there was nobody in the A-List check-in line I'd ask the ticket agent to put me on the list (saving the time to get thru security and find a GA/CS), and 2 out of 3 times they didn't do it (or do it "right") and I wasn't on the list by the time I'd gotten to the gate.

The app now helps verify that now, and I now have CLEAR to augment Pre (which means "September 10th"-style security wait times at SJC for me) so I now just wait 'till I get to the gate- but a heads-up, just-in-case.