Wiring multiple ESP Fireline detectors to a single zone

[Orinoco]

I\'m trying to wire 3 ESP Fireline smoke/heat detectors into my Comfort system and I\'m having a little trouble deciding where to put the resistors. I\'ve looked at the wiring diagram for four wire smoke detectors in the quick installation guide and I believe I can follow it to connect each detector into a separate zone, but I don\'t have enough spare zones to allow that - I need all three connected together into a single zone.

I have the optional relay bases for the detectors so I can use the wiring diagram from this 2 page pdf:

ESP PSD212 manual

I just need to know where to put the 4k7 resistor (or resistors if more than one is needed). Any suggestions?