You do know that your instructor's FI rating expires at the FIR boundary, don't you? So even if he lets you fly the LFAT ILS in simulated IMC, you can't log the time as P/UT, and it can't be signed off as a satisfactory ILS approach in your logbook? (Indeed I'm not sure about the legality of simulated IMC in French airspace anyway.)
For that matter, once you have the IMC rating you can't use it in France, either...
Tim