The apple watch ECG corresponds to lead I. Lead II and III is right and left arm respectively to left foot, so they will be possible with a bit of flexibility.

The apple watch ECG corresponds to lead I. Lead II and III is right and left arm respectively to left foot, so they will be possible with a bit of flexibility. The 6 precordial leads are not possible, since they are measuring the voltage between an electrode on the chest and the mean of the 3 extremity electrodes.