"91.175 forbids it"
I did point this out to the FAA instructors and examiners in the USA recently, and their view is that this applies only in airspace where you need ATC clearance for flying the procedure.
In the USA, one has Class E down to a very low level (700ft or 1200ft; I can't remember the rules) which means that most or all of the IAP will require ATC clearance (because E is CAS for IFR).
But if you did the descent wholly in Class G, the view was that you are free to do what you like.
In any event, one can legally fly
at the MOCA, which (in non-mountainous terrain; another expression which means one thing here and another over there) is 1000ft above the highest elevation within 4nm. This amounts to a DIY IAP with a 1000ft MDH, doesn't it?
"Pressumably, this would need to be done with someone who is both a CAA examiner (for IMC renewal) and an FAA instructor qualified to sign off the BFR in an N-reg aircraft."
One can do it all in a G-reg, but for JAA stuff needs a JAA instructor rating, the FAA BFR needs a FAA CFI rating, the FAA IPC needs an FAA CFII rating, doing any
paid work in any aircraft reg in UK airspace needs the JAA instructor rating, and doing any paid work in an N-reg needs the DfT permission
There are dual JAA+FAA instructors around, but expensive, and you still need the DfT permission of doing it in an N-reg (unless he does it for nothing).
I hope I got that right.....