I'm pretty sure you can fit them then drop the hardtop on. The mounting posts are of course under the rubber covers that can be seen in front of these infills.
Strangely I actually had a set, never tried them with the hardtop then sold them as in the Summer I would either get soaked getting out to remove them, undo all the one button functionality and practicality, or simply forget to take tham off and rip them out of place
One of the best improvement in appearance on can give his Z in my opinion. Also reduces turbulance and noise at higher speeds. Never drive mine without them when the roof is down.