Last one I had was yesterday night, on a CRJ200.
upon boarding, the captain and FO were already in the cockpit, but I went straight in their direction (the F.A. was talking to them, so the door was open), and I boldly asked "Good evening sir, I am a privot pilot. Would it be posible for me to give you a visit during the flight ?"
He said that he would call me when we would arrive to the destination.
During the flight I wondered whether he meant before or after landing, so about 30 minutes before landing, I went again to the F.A. "Sorry miss, could you ask the captain whether..." she asked me to wait a minute, went to the cockpit, then came back at me, "please follow me", I went into the cockpit, and voila, she drew the jumpseat for me.
Follow my advice, always ask, and also, always insist (sometimes they say yes, but they forget during the flight (they have other things to think of)).
And if you're lucky enough, seat down, enjoy the ride, and speak only if they speak to you (remember that they are working)
Antoine, still in the sky