A downward departure may be appropriate if the defendant (1) has completed serving a term of imprisonment; and (2) subsection (b) of §5G1.3 (Imposition of a Sentence on a Defendant Subject to Undischarged Term of Imprisonment or Anticipated Term of Imprisonment) would have provided an adjustment had that completed term of imprisonment been undischarged at the time of sentencing for the instant offense. Any such departure should be fashioned to achieve a reasonable punishment for the instant offense.