The triple FD should work same as the double. Don't worry about guestimating where the granny gear would be. Try disconnecting the cable then reset the low limit screw so that there is a two millimeter gap between chain and the inside of the derailleur cage. Then reattached the cable and adjust tension as needed with barrel adjuster. Should work.
That is essentially what I did and by doing that it completely eliminated the lowest step of the FD (where the granny gear would be). Is this right?