They changed this some time ago - there are now boarding card checks when you want to enter France via airport from the Swiss side (I think there was a thread on this in the Swiss or Air France forum).
Hence not possible if you do not have a valid departure boarding pass.

However, last time I checked was almost a year ago, since I have been grounded since then
I also think that the French sector is still closed completely and flights to France depart from the Swiss section - you can check on gva.ch for flights to France (e.g. Paris) and if the gate doesn't say "F..." then it's not from the French side.