I'm using this Maisto Citroen 2CV as a demonstrator:



It also has one of my pet hates, the headlamp lens is attached with a stalk:



I'll take care of this too.

Pop, pop, lenses and reflectors come out:



Poor eyeless ugly duckling:



Reflectors with lenses:



Pry apart:



Cut stalks off:




You need these beads:



This is a lifetime supply and then some. I got this bag full for 2 quid from my local craft shop. They come in all kinds of sizes, so you can select suitable ones no matter which scale you are working in. These that I have are as good for 1/18 as for 1/24-25 scale.

Only two beads are needed:



Also needed are two dressmaker's pins:



Tamiya Clear is used as a glue:



Simply on the grounds that it sticks very well and will stay clear until long after the last archeologist died.

Glue the two beads onto the two pins with Tamiya clear like so:



Glue the pins with beads into the reflectors with Tamiya Clear like this:



After the above has dried, glue the lenses back to the reflectors with Tamiya Clear:



Cut the pins flush with the backs of the reflectors and glue the whole shebang to the model with - you guessed it - Tamiya clear.

The effect is very convincing:




I did essentially the same with my Welly Peugeot 504:



You see, it works with any shape and any size headlights.