airtags, an employee of QF group is OK for jump as long as no seat is available in the cabin (a few exceptions to that but nothing that goes against the basic principle). Therefore if the CEO has a QF ID (and I presume he would?!?) then he can ride the jump if there are no seats available in the cabin. It doesn't need to be an airside ASIC per se. However, once on board, he (or she) can't just come up for the take off or landing. Once you're on the flight deck you're effectively staying on the flight deck. Once you've left the flight deck for a seat in the cabin (if available at the last moment after having previously allocated JS1 or JS2) you're staying out.
Some nations do have exceptions to the philosophy above and simply won't allow anyone but the crew on the flight deck in their airspace or on services to/from their nations.
Now that I've had some time to mull it over I can actually think of operational reasons to have the CEO on the flight deck but then the above rule comes into play. It's not a 'come and go as you please' type deal. It's a 'come up before flight but you're staying up' type situation.