I know what you mean, they seem a real after thought.
Mine just about locate to the hood mechanism, but I'm never sure they stay in pace during roof operation. I would not discard them, Porsche only put them there for a real purpose, but I think it is simply 'water-management' to keep excess rain of the hood arms/pivots.
There are no obvious clip positions or fixings, they simply hook to position. It is a case of patiently trying different positions to find the right one. Several shields on the 987.2 are like this, the front boot side trims are weak clips and Velcro...