Hmm would it be possible to custom mount a bullet lamp to the fender as those old French road bikes did. I was thinking get the after market fenders on the road bike. Drill a hole in the top of the fender and attach the lamp and bracket via a very short bolt with a thin nut. If nut thickness became an issue I suppose the nut side of the bolt and nut set could go on top of the fender. The only issues I see are whether the fender is too thin across and whether the bolt will rub on top of the tire. I figure the wire leading to the lamp could be threaded along the underside of the fender and protected from spray via a casing of electrical-type waterproof tape. hmmm tricky I think but possible? I'm not sure yet.
I don't have the brazing and welding equipment so those options (which the peugeot co probably did) aren't avail. to me.