Talos:

in the Greek case it's not that Greece is forbidden to buy back part of its debt in the going rate (at 70c to the Euro), just that it cannot use the Special Fund's money to do so.

A possible solution that is a win for Greek oligarchs and a win for the Greek Govt. and people:
Make a deal with the oligarchs that they buy the debt at the best price possible, (rumors of default could improve their price), with the agreement that the Greek government will then buy the debt from them at a few percent above their purchase price. Retiring loads of debt would increase the credit rating of Greek bonds which could be issued to the oligarchs as payment, which  would, to say the least, greatly depress the value of CDSs on the original bonds, so one or both parties could sell CDSs short prior to the transaction. What is good for the goose is good for the gander! :-)

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