At Alaska, the captain owns both jumpseats inside the cockpit. If you have been given a cabin seat you are no longer listed as a jumpseater. There is no way for the flight crew to know that you are back there and the captain has zero say on who rides in the main cabin. The CSA owns all of those empty seats and does with them what they will. I never mind if someone wants to stop up but could care less if you walk on and turn right.. And if you are an Alaska pilot just walk on go find your seat. No need for awkward niceties at all