I haven't used it yet, but maybe there is a method you might find useful.
BlockChain.info/wallet has a "desktop sync" feature in which you configure your client to act as a server and accept RPC commands. Then the BlockChain.info/wallet plugin will grab your keys from your wallet.dat and sync them by copying them to your BlockChain.info/wallet
You don't need to have the client current with the latest blockchain download for this to work and it doesn't use the Bitcoin P2P network so this should solve your problem.