I do not think you can. This was in the techie news a few weeks ago, and immediately, the next time I tried to log in to my Google account, I was required to verify the secondary e-mail I gave them in 2006 was still correct. They warned in that opening page, that if I did not provide a secondary e-mail, and I forgot my password, I would not be able to retrieve it.
The best place to get a real answer would be Google G-Mail Forum help. Lot's of Google staff are there waiting to answer questions and assist.