I have always wanted to do this so will be very interested to have a look at TypWiz 4 when it is introduced this spring. :D
http://pinns.co.uk/osm/typwiz3.html
(http://forums.gpsfiledepot.com/index.php?action=dlattach;topic=3294.0;attach=1250;image)
This does seem like its right up your alley :)
Didn't know anybody but Garmin had a genuine NT compiler.
NT-compatible .typ files doth not an NT compiler make. ;D
The online .typ editor has supported the NT .typ files for quite some time. I never tried to understand what the difference was myself.