I don't think anyone makes an adapter to mount 6x9's in a 6.5 hole.
I checked the metra site and they don't seem to make one, and they make everything.
I see these 6x9" spacers on ebay. Maybe you could adapt something like this?
http://cgi.ebay.com/ebaymotors/NEW-S...737#vi-content
I still don't see it happening without cutting up the door and the inside the of the door card.