It appears the I2C bus sniffer, macro (2) in the I2C library, may have been working all along. aphoticjezter writes in the forum:

I hacked the binary file to change the bitrate for one of the speeds to 230400, and I also used RAW mode as suggested.  So far I seem to be reliably sniffing the traffic…

The key is getting data from the Bus Pirate to the PC fast enough that we don’t miss any I2C signal changes. One way to increase the speed is to change the Bus Pirate display mode to RAW, and then have your terminal show the HEX equivalent of the raw byte values. In raw mode the Bus Pirate doesn’t have to shove 5 or 6 ASCII bytes up the wire for every byte snooped.