Its not common but not unheard of.
I have done it in the past when a PPL and his PPL mate were in the front I fell asleep in the back and the pair of prats managed to get themselves into hole of VMC with no way of getting out unless going IMC after deciding to change the route from the east coast to up the A9 mid trip, because it looked OK.
It was in a C172 and getting my fat arse into the front produced a stream of terrets strength swearing at the pair of prats and the aircraft.
Lesson learn from that though, not much point having an IR onboard if they can't get to the controls. I did consider leaning over and pattering instrument flying from the back but went for the get in the seat option. Still don't know if getting in the front was the best option.