I work for US. I apologize ... you just got a cranky gate agent. You simply show up, fill out a form, and the gate agent will list you, verify you in CASS, and clear you to either a passenger seat, if available, or the jumpseat. The procedure to list you in QIK/Shares takes about 30 seconds and is necessary to run the CASS query anyway. MYR frequently has full flights and has plenty of commuters.
The only mechanism to pre-list on US is for mainline pilots - we can reserve the jumpseat in advance.