If you will review the Linux kernel sources you will notice that there is absolutely no support for I2C slave - I guess this is logic since it is very rare to use a Linux base system as I2C device. It is also not simple because the Master may have timing issues.
But, unfortunately, sometimes it is required - so, if you are using Freescale's I2C controller (of course it can be done only with a controller - do it with GPIOs is much more complicated) I can help you.
I did it for device based on Freescale's PQII pro MPC8308 chip that is based on PPC core, but I believe it should not be a problem to do it also to other Freescale's chips that base on ARM core and has the same I2C controller unit.
I hope to expand the information on that issue here, but anyway if you need help, I'll be happy to assist.