By John O'Donnell and Paul Carrel FRANKFURT (Reuters) - European Central Bank officials are considering ways to ensure weak countries that stand to gain most from a fresh round of money printing bear more of the risk and cost. Officials, who spoke on condition of anonymity, have told Reuters that the ECB could require central banks in countries such as Greece or Portugal to set aside extra money or provisions to cover potential losses from any bond-buying, reflecting the riskiness of their bonds. Such a move could help persuade a reluctant Germany to back plans to buy state bonds. ...