Topic: I2C - how to set 400kHz?

The infocast and Chumby hacker board have I2C, but they operate at 100kHz and I need to read 115kBaud from a ATtiny4313-as-UART.  It works, but I can't empty the chip fast enough at 100kHz.  I don't see an ioctl, and both timing settings are commented out in the linux source tree I have.

Is there an ioctl or something else I can do to speed up the I2C to 400 kHz?