I follow a lot of auctions on Ebay for ancient 
art, and MOST of those auctions are "private" to 
keep people from hassling ANY of the bidders (not 
just the high bidder). One thing that is almost 
always in the item description is something to 
this effect:

"Bidder IDs are kept private to protect bidder's 
identities. On occasion, a high bidder will back 
out of their bid. Please e-mail if you would like 
to be considered as an alternate winner should 
this occur. Remember that if you do not e-mail, 
your address will be inaccessable in the event of 
a high-bidder backout."

This way you would have access to the address of 
anyone interested in being considered as an 
alternate winner. (My guess is that everyone 
would write to you! ^_^;;)  That might solve your 
problem for any future "private" auctions. ^_^

Many Sharp Smiles,
--Drac