[Proj] adding a local EPSG code

[Hamish]

Hi there,

I am wondering, what's the recommended best-practice way to locally add a
new EPSG code & have the proj4 toolchain pick it up?

do I just pick a suitable number and append it to the end of 
/usr/share/proj/epsg? I'd prefer to add it to /usr/share/proj/other.extra,
but how is that file used? does the code need to be in the file at proj4
and gdal build-time in order to work?  (same Q for the fate of the esri &
esri.extra files, out of curiosity)


fwiw I'm dealing with a nationally known handy-projection not a personal
invention, but probably not up to the popularity that would warrant
submission for official inclusion to whatever the EPSG call themselves
these days. just another local tmerc, but one I'd like to have on all
the local machines..


thanks,
Hamish