If I have a constant BAR in Foo, which I will use in a class C I\'ll have to write
Object o = Foo.BAR + \"...\";
which I can use Ctrl-Shift-M i
Eclipse can do a global search and replace with regular expression over all files in the project.
To add the static import at the beginning of all files you could replace the package declaration by itself plus the static import.
Then do a project wide organize imports, and you're all set.
Be careful, though, this could also make a big mess if you do it wrong.