I made it much easier:
I told people that I usually log out in directly after a dungeon and don’t really bother going out, when I’ve got stuff to do. If you log out of the game in a dungeon, you will stay marked as online in that dungeon until you log in the next time. And if anyone sees me online and in Sohm Al again afterwards I say “I’m farming grand company seals and this is the best method for me to farm them.”.
That’s what I did when I was leveling all jobs to 70 and no one bothered.