Finally, I couldn't use an ATtiny as it wasn't as powerful as my simulation needs it to be. I should be working on high frequencies.
So I will end up developping some bit banging I2C slave driver for Arduino or other since it will be hardware independant.
Can anyone tell me from where to start and if there are some examples or samples to begin with? I found only bit banging drivers for masters or for slaves written in asm.. I should write sth in C.