Don’t know about Alpes D’Huez, but spent a few days in the three valleys (Meribel, Courcheval etc) in August last year and nobody gave a monkeys what anyone was or wasn’t wearing. Load bike onto chair/Gondola, go up hill, get off and ride down hill again. This also applied to Tignes and Les Arcs.
The runs in those areas were a lot easier than I expected. To clarify, they could be very hard if you wanted to ride them very fast, but if you wanted to pootle they were all rideable/rollable. This applied to the reds. Not sure if this helps, but I’m not convinced that the French would be particular in enforcing the FF rule.
With regards to taking FF on Easyjet, me and my mate just attached them to our cabin baggage rucksacks and nobody said a word. Be aware though that they enforce the bike bag weight limit at Geneva. I had to repack and dispose of a couple of unnecessary items…