While you CAN submit the application without the FBI request it is advised to NOT do this. If CIC decides to send your application back to you as incomplete they would be well within their rights to do so. That would force you to resend your package again once you've received your certificate, which would also require you to update any outdated forms and such.
The guidebooks are given for a reason.They state a COMPLETE package should be sent, not a partial package, not a package with everything except, but complete.
I personally wouldn't take the chance, since they might be a month or more before they decide to actually open your package and find out it is missing stuff and then throw it back in the mail to you.