When I tap harmonics I tap them like this: If I hit an open E string, I tap lightly the 12 fret just above the iron wich makes an octave and so on. There must always be 12 frets between to get them. So if you play G note (3rd fret on E string) tap lightly the iron on 15 fret wich is also G (octave).

here´s the tab:

A-string |--3----t15--|

Now, I´m not sure if you ment this but if you did than this is the only way to do it. Good luck.

PS/This is easy.