There are several ways to turn the engine when setting rocker gaps. The usual are:
To turn the engine by grabbing and pulling the fan with one hand whilst keeping tension on the fan belt with the other.
Putting the car in 4th gear then with the handbrake off rocking / pulling or pushing the car to turn the engine. Both of these 2 methods is easier with the spark plugs out – although i usually leave them in!
Or as i found this method on the internet to use the starter motor to nudge the engine over – without the ignition on. The picture shows a permanent switch being fitted but a temporary switch can be used. Simply connect to the input / output wires on the starter solenoid going to the starter motor.
Although this method may take less effort i can see it being a bit hit or miss – may not do the starter motor a lot of good either.