Hey Andy-
When I used to live in Hawaii, we put the inspection stickers on a metal bracket that hung from under the bumper. Lots of people who actually care about their cars do this and nobody (including the cops out there seem to mind).
Basically, they have an outdated law out there - it says that the stickers must be put on the bumper, and of course it was enacted back when everyone had chrome bumpers. The bumpers of most all modern cars (the NSX included) are hidden under painted bumper covers, so perhaps it can be said that 99% of the population out there is technically in violation....!