Well here in Aus a turn and balance is mandatory for aerial work (including flight training) so it shouldn't happen
Have heard a story of someone using a water bottle on the dash as a makeshift AH, interested to see if that works
Otherwise get them to power back to idle, and push forward to 500'/min RoD or so, and then keep wings level by seeing if the DI is turning. Thats all I can think of, and it's probably what I'd do if I ended up in that situation