The 18F MSSP has a "Multi-Master" mode for the I2C bus. I've never used it, only know about it from the 18F4620 datasheet and spending a lot of time reading the Phillips I2C Bus Spec Sheet a while back.
It might be worth doing some study. I could be easier to implement than we first realize, especially with 2 PIC in the same basic family (18F).
HTH,
Steve
EDIT: Here is a new link for I2C Specifications. There is a link to a new .pdf file for the bus specs.
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