Ah you have a point. Since we are talking about own libraries, that are not "OS installed" it would be nice to avoid full paths in the project, but as you point out, we can add it globally to the .bm file, and since it doesn't hurt to have -L/path on programs that don't need it, that would be just fine.
Lund
You can also consider separate build method if having it there all the time would hurt...