Hi
Firstly ask for extension close to deadline ....i.e 14 or 15 April.
Secondly FBI usually say that it will take 1or 2 weeks but it will take lesser time. They just don't want you to bother them again and again.
Thirdly write email to FBI close to 10 April and ask the status of ur application. They will reply back ....something like they will take 1 week or 2 weeks to complete processing of ur FBI. Use that reply to ask extension from CIC. Let's say FBI said 2 weeks. U will ask CIC to give u extension of 4 weeks as it will be 2 weeks plus mailing time. You don't even have to mention the certified cheque story. Just be to the point that u application is close to processing....as per reply from FBI it will take 2 more weeks . Extra time will be required for the mail to reach. Kindly grant me extension of about four weeks. Something like this u can write.
Let's say u ask for status from FBI on 10 th ......no need to wait for reply. Just after sending email call them. Ask status and also request them to reply ur email .....explain them that u will use this reply to ask extension from CIC. They will reply u just after u hang up. I did this twice and both time they sent reply immediately after call.
Also keep calling FBI and keep requesting them to process ur request faster as u are close to deadline. They are nice and usually agree. I mean in ur particular case. U know they don't entertain faster processing otherwise.
I will easily work out. Don't worry. CIC has been very cooperative. Just obtain an email from FBI about how much time that will take. U need not over confuse things by talking about fee and all.
Good luck