This is a question of can it be done and I'm not so familiar with the hardware to see the answer.
The basic question is, can I use PA6 for SDA (I2C/TWI) while using Timer1 in FAST PWM mode?
I'm assuming code will be needed to set and clear the pin where I want PWM to appear so I don't need the actual OCR1A output which maps to PA6. The data sheet doesn't quite seem to answer the question of what happens when you try to use TWI when the timer is in this mode, or at least I don't see it.
I'm sure there are other ways to solve the problem, but the question as posed is what interests me.