H1B visa transfer in case petition document is lost

USA H1B Visa
1

Hi

I am currently in India and have H1b visa stamped on my passport which is valid till Oct 2015. I had also travelled to US on this visa in 2011. Now, I have changed my job and my new employer wants to get this visa transferred. Is it possible to the git it done if I dont have the old petition documents available (like I-797) or only the stamped visa on the passport is enough for a transfer?
2

Do you know the receipt number? If yes, then it can be done.

Do you have a copy of the old approval notice? If yes, then it can be done.