Bit Banging a PICAXE 08M2 as an I2C Slave
With one master node  and multiple PICAXE-08M2 I2C slaves, "diode-mixing" approach may be the easiest/cheapest solution or substitute an X1 chip.


single pull-up resistor for the comm. line Ea
each slave connects data via anode of Schottky diode &amp; cathode to PICaxe
PICaxe input is connected to the comm line via a 10K resistor
Use simple SEROUT and SERIN operation with qualifiers to address each node
many others have implemented such a Serial protocol, so don't reinvent the wheel.


Grounding, shielding, impedance control and low capacitance wiring is essential. eg 7pF/ft

can you say let's have a party line?
Consult with those who have done it, after you try it.