I used this method recently when, for some reason, Ebay would not let me send a second chance offer (said the bidder had to be an underbidder, which he was!).

If you click on the bidder's rating number, Ebay takes you to their Ebay Rating Card. If you then click on their Ebay name, Ebay will ask you to sign in again and then it takes you to the Contact an Ebay Member form where you can send a message.

Incidently, the bidder I contacted was very happy to have been contacted as he had opted to accept second chance offers (you can refuse) and so we did conduct a sale - we tried doing it 'officially' through EBay, but Ebay failed us!

Jason