Homebrew approaches, what an extremely stupid idea. Either fly IFR and carryout a promulagted approach or fly VFR, don't go making up your own procedures.
I'm sure there are a few clever people who can figure out something, then there are the rest of us who are not so clever and miss an important item.
One thing you cannot incorporate in a home brew GPS approach is the scaling required to give the accepted scaling requirements that occur in a promulgated GPS approach.
Isn't the problem with GNSS approaches in the U.K. more the requirement for approach trained controllers? Whereas the USA allows you to shoot an approach to a non-towered or closed airfield with a clearance from a controller many miles away, so the only cost is the survey and approach design (and many early GPS approaches were overlays).
Isn't that so quaintly British, find a difficult solution to a simple problem. What benefit does the controller provide?
In New Zealand, (and I suspect it's the same in the USA) no controller clears you for an approach located outside of controlled airspace. You will be cleared out of controlled airspace and then you will carry out the approach as promulgated in the AIP. No controller input required.