Many RWYs have a holding point 'somewhere in the middle' or at least not near the beginning of the active. Switching from Ground to Tower (without being told to) and hitting '6' works fine and I realize that the word 'backtrack' is not in the voice sets. Since PF3 'knows' where exactly my position is while taxiing, and PF3 'knows' the layout of the airport, it must be possible for PF3 to discover that the aircraft is at the holding point for the active runway and switch from ground to tower in time and afterwards give a takeoff clearence. But hey, that pure luxury.

When I'm in line behind AI at the holding point I get the 'line up' call right after the AI departed. Nice. But that is directly followed by the takeoff clearence. There is a 2 minute rule for bigger aircraft. In my case I was cleared for takeoff (Q400) right after a departing C206 (or something small like that). If I had not waited for at least two minutes, I probably would have come very close to the Cessna (Traffic, traffic). Would be nice if PF3 waited a while with the TO clearence.
Dirk