Bugger!
The CAA don't insist that you hsave it revalidated three months early.
They (JAA, not CAA) offer you the opportunity - just in case you have trouble finding an examiner at last minute.
Now that it has actually expired, it's (legally) "game over". Proficiency check with an examiner.
With regard to backdating the signature - illegal. If *you* know anybody who may do it for you, you ask them quietly in a dark corner. Don't expect to get a "Yes" answer on these public pages.
If you asked me..."No!".
I'm afraid it's another one of those real life lessons in responsibility.