May the Force be with you!
It can be done though despite the two hurdles you are likely to encounter in this country: bureaucracy and arrogance (only the French know how to fly kind of thing).
Until EASA flight crew licencing is implemented, you still need to have your UK JAR licence "validated" by the infamous French DGAC. Here's the link to the form to fill in:
As far as your FI(A) rating is concerned, I believe that you have to undergo an assessment and some FI training and a test to be able to instruct on a French registered aircraft.
You can drop an email to the DGAC: firstname.lastname@example.org
L'ESMA was looking for flying instructors able to teach in English (as they have Chinese cadets training in Montpellier) some months ago.
Good luck and please keep us informed of your progress!