Jumpseat -
afaik as an flight deck member you can always ask for a jumpseat(own company only of course). If the cockpit crew is really happy to have you all the time in "their office" is a different story.
I always hate when someone sits in the flightdeck jumpseat, especially if it is a TRE (lol).
So yes, based on Captains approval you may get the jump.