Does the PICAXE support arbitration that would allow two masters to use the same I2C bus? If not, would it be possible to use an analog multiplexer to alternately hand over control of the bus to one PICAXE at a time? There would of course have to be an I/O line between the two controllers for synchronisation. Arbitration or multiplexing would enable a simple form of multitasking to be undertaken by using a number of PICAXE chips on the same system.