An effective technique is to draw their attention to it.
Most manufacturers are out of touch with new regs. A few years ago I phoned up and then faxed the marketing execs of all turboprop and bizjet manufacturers, drawing their attention to the then DfT proposals to kick out N-reg planes from the UK. Almost none of them were aware of it... Socata and Pilatus were not aware, amazingly.
When the EASA version came out, I did the same exercise. Socata were by then aware. Cessna were not, and they said they will take it very seriously.
EASA makes a big point of not being influenced by commercial interests, which is why their committees are mostly anonymous, but this makes them vulnerable to having a lot of "work" trashed at a very late stage, when it is realised what they have done.
With a bit of work, this GPS approach operational approval will also get trashed because it is so totally barmy, but it won't happen without some concerted effort because if EASA is left alone they are capable of anything no matter how stupid.
BTW, both EU-reg and N-reg are equally affected by this, especially as the NY IFU is almost certain to wash its hands of any approvals. They have already washed their hands of avionics 337s etc.
The upshot will be that GPS approaches will become legally unusable, even for aircraft with an existing approved GPS installation, forcing people to fly the conventional-navaid approach but obviously using a GPS, which is fine but hardly the point, and is a longer track because you have to go through the charade of flying the outbound leg, etc. It will also result in published GPS approaches being flown as "VFR", and in more DIY approaches being flown.