Can you backdate a SORN?

[RB Will]

It's probably no but thought it worth asking.

Short details.
Car threw a cambelt in July 2014, recovered by AA to a local garage who have dragged their heels over it and now told me it's going to be very uneconomical to repair so going to break the rest of it to salvage what I can.

Can I backdate the SORN in the hope of getting 9 months tax back rather than 2? It's a £200ish difference. Would the report from the AA essentially saying the car is scrap go any way to showing the car has not been used since July?

Thanks for any help.