How to get co-signer off the hook?

I borrowed a $50,000 student loan with a co-signer two years ago. That person was a nice guy and co-signed the loan without complaint althougth he was not my relative. The loan, however, becomes due this year and shows on his credit report as private debt. He wrote to me asking when I will be able to pay it back. My monthly minimum payment is something like $300. I know that as long as I'm not late on monthly payment, his credit won't be affected. However, I want to get him off the hook as soon as possible and will feel guilty about putting him at risk for 20 years. Although I've started working and have a pretty decent income, to repay $50,000 debt within short period of time would be impossible. Any advice?