One 'fairly simple' approach might be to use a scale designed to be stood on to weigh people, place under crank, use your
pipe+8mm allen wrench in a horizontal position and use a large enough piece of wood of the right length between the 30cm
mark on the pipe and the scale and as you press down on the pipe at the 30cm mark you can read the weight directly and
hence the applied torque. A 7-10cm sq piece of wood should be stable enough, and a small V in the top will cradle the pipe.

Of course you will have to apply counter torque to the crank, which can be a problem depending on the crank/pipe angle.