Here is a new paper by Fratzscher, Steffen, and Rieth (pdf), advocating gdp-linked loans for Greece.
Here are older proposals for gdp-indexed bonds (pdf). Scott Sumner comments on the new Greek proposal. Here is an IMF paper on the topic (pdf). Greece already issues some gdp-linked warrants. Here is Argentina fudging its gdp stats to save on its gdp-indexed bonds. Here is more on related disputes.
p.s. they are not going to do it.