If I were Emperor of Europe here is what I would do: I would have the European Central Bank (ECB) implicitly guarantee Greek debt by offering to buy Greek debt at some particular interest rate and then pay for the purchase of Greek debt by issuing a "Eurozone Bond" backed by the full faith and credit of all the countries in the Eurozone.
The buying of Greek debt would not be inflationary since the ECB would effectively be sterilizing the purchase of Greek debt with the issuance of Eurozone debt. It would also relieve the fiscal pressure on the countries who are putting up government funds to help shore up the Eurozone. These countries could still--in partnership with the ECB--exercise control and impose all the austerity conditions they want.
This would also help push the Euro ever so slightly toward its full potential as a competitor currency of the dollar since it would finally create a true Eurozone debt instrument. Obviously, though, the market would not be very large or liquid but perhaps this market could be opened up to other countries. While the EU does not seem overly concerned with the problem of moral hazard it would be relatively easy to limit countries from taking advantage of this market if the EU actually started to enforce their rules governing debt to gdp ratios.
I am double minded about what interest rate to charge the Greeks. A penalty rate seems appropriate, but obviously that may only make it more difficult for Greece to pay down it's debts. At any rate, some kind of risk premium above what the ECB would get on the Eurozone instrument seems appropriate and would be profitable for the ECB. And if the Greeks finally do default? Well, then the Germans can put their real money to work.
Perhaps unfortunately, I do not run Europe and the ECB seems like a profoundly conservative and unimaginative institution. That may be a necessary thing in Europe, it may also be a major liability for Europe to have monetary policy nonexistent at the national level and unhelpful at the supra-national level. While the ECB has been engaged in what the Wall Street Journal calls a "stealth bailout" of Europeans banks holding Greek debt they may do well to push things further. Legal and political realities notwithstanding.