It seems to me that the major function of central banks in foreign transaction clearing is to allow only the net difference to ever have to be transferred. But the sticking point will always be the case of persistent current account deficits with specific countries. So European national central bank to national central bank clearing could work so long as the current account balances remained close to zero or within a range deemed acceptable by the bank carrying the deficit. Such an arrangement would tend to make such deficits either self limiting or at the discretion of the surplus country, as is the case between the USA and China. Such an arrangement might be a little too obvious to suit the desires of Germany, however.

"It is not necessary to have hope in order to persevere."