Well I just louvred my bonnet just above the inlet manifold and rear of the radiator. According to my readings it has lowered the charge temp noticeably. Ill do some more extended readings over different conditions once its back on the road again. However the inlet manifold is a lot colder now and it doesnt overheat in traffic. On a standard NA 16v the situation would be different though, my bumper isnt standard and Ive got an oil cooler and a chargecooler rad in the front as well as the standard engine radiator. Best bet would be an exhaust vent above the induction kit I would have thought. As long as you can get some airflow in through the front and its got an exit route out through the bonnet, thatll create a local zone of colder air passing through the bonnet area that the induction cone can draw on. Without running the whole system inside a sealed airbox, it would be difficult to be sure that it would work. The only way to find out is to try it for yourself and see, bearing in mind none of us are full-time experts in aerodynamics and even if we were wed need to do a lot of testing and experimentation to see what worked and what didnt.
The only thing that does make sense to me is that putting a bonnet scoop in wouldnt work at all, if the aim is to get cold air to an induction kit. Theres not enough airflow through the engine bay to make it work. The primary airflow through there goes in through the radiator and then out underneath the engine and gearbox. So if you put in a bonnet scoop it needs to pull air in and exhaust it below the engine. A bonnet vent would work though, if it were close enough to the radiator and just above it. Likewise, an air duct through from the passenger side wheelarch/bumper onto the air filter with a vent above it in the bonnet should also work without disturbing the rest of the airflow.
I could be wrong though!