Audi R8 Headlight installation help

What is your question?

I have a set of Audi R8 headlights that I would like to put on my A6. They are just barely too small leaving a slight gap between the bumper and turn signal. I don't want them to bounce around as I am driving therefore would like to know what the best material is that I should use to mount them so that they fit snug? Thank you for your help!