Great question...

In the ebay auction southhams ran before the one that I actually "won", I noticed that he edited his listing by mentioning that a bit of modification might be needed to allow the sensor to poke through. Subsequent listings have not had this edit.

But after mating the inserts to the actual grill and then putting them back on the car, I found that the sensor did not poke far enough out to need any modification. It's immediately behind the insert and functions perfectly.