Do not know if it still works, but WAAAAAAAAAAAY back when Term A had separate security for (mostly, maybe all CO and non CO sides) I used to go to President's Club on CO side (of course another change, I'm not sure you can enter without a CO UA flight), and reclear with same BP to other side to fly US Air (of course they would always tell me I am going to the wrong side to fly US Air).

Those were the days ...... hopefully it still works as posted above.