Since I do not have this kind problem, so that's just my two cen

You may draft letters first, than contact the editor and society presidents. Once they agree, you can send the letters to them (they like this way). You do not need to exaggerate what your situation is, just ask them to write a letter to indicate your contribution. That should not really bother either of them, but since the letters are from editor and president, they will be considered when officer evaluate your case. What else can prove if the officer does not trust the letters from editor and president?