I'm looking for a way of adding tone marks above characters. It's fairly easy to add Pinyin with tone marks, but I want to add only tone marks. I want to use this as a teaching tool, because even though most students don't have a big problem with the syllables, they do need to focus more on tones. Thus, adding the tone marks would mean that students can focus on the characters while still being able to see the tones if they need to and focus on them more.

Right now, I have to do this manually, which is quite tedious. However, I'm guessing that there might be a way of doing this automatically. Perhaps there are fonts that display the tone diacritic next to the character? The problem would be characters with multiple readings, of course, but perhaps there is a way around that. Does anybody know of any other way of adding tone marks above characters without having to do it manually?

This is done both in Practical Audio-Visual Chinese and New Practical Chinese Reader (can't remember exactly where it begins and where it stops, though), but I think they've done it manually using some kind of typesetting tool. The best solution would probably be to use Ruby annotation and somehow get rid of the Pinyin/Zhuyin and get only the tone mark. I don't know if that's possible, though.