Wait until the last moment to submit your application, and include a LoE indicating you have requested it & show proof you have requested it (receipt of payment, postal receipt, etc).
I would follow Mgnlky advice on this one as it is the exact same thing I did. I have not seen a response from CIC yet other than the AOR but based on the response of other applicants, they usually get an extra 60 days. With the recent draw coming up at 458, I'd be very hesitant to decline and get back into the pool.
Agree with the above, because CIC is aware of FBI's extremely slow processing times and will very likely give you an exempt as long as you can provide as many proofs as possible that you are well into the process of applying. Even better, try calling up the FBI, get a contact name, where they are at with your application and provide those details to CIC. Good luck