Another way we sometimes "cheat" for non standard foreign accents:
Type the dash, em dash, whatever you want before the letter you want the line over. Select that line and baseline shift it to the height you want. Then highlight the whole line and kern (minus) until the line falls above the letter. This will put it right over the letter. Next, because the kerning affected the previous letter, put the cursor between the previous letter and the line (don't highlight) and kern (plus) it back out again. It works fine for us for a few special marks we need. If you need this often it may be too much work however.
