I would like to add aeiouAEIOU with straight dashes ontop of the characters (like macron marks). These signify long vowel sounds and are used in the Hepbern romanisation of Japanese Language called Romaji.

Looking at a Japanese "Pro" Font:
Unicodes seem to match glyphs for tilde diacritic characters
cid reference codes do not seem to work?

Is there any way to make Romaji work in a font without doing a special function OT feature?