I2C on a CBC v2

The manual for the CBC says that there is I2C interface with additional hardware. Has anyone used i2c with the CBC v2?

My goal is write up a basic program that uses a Wii numchuck as a controller for the CBC. This would allow the students to focus on the building of the robot without worrying about the code to control it. I wanted to focus my team on some basic tasks of building tools with last years parts to manipulate common Botball articles like foam blocks, foam balls, puff balls, etc.

Thanks,
Brad A.