Hmm. Learn something new every day around here ...
If you have Arial Unicode MS installed (or possibly other unicode fonts) you
can do this:
Choose Insert, Symbol
Choose Arial Unicode MS as the font
Choose Latin Extended Additional as the Subset
There's an R with overbar/macron as one of the characters there (1E5C)
Or in the Combining Diacritical characters set, try the Overbar. I didn't have
much luck using it with capital letters but you might be able to make the R
slightly smaller and fool it into working for you.
