so after 72 hours the transaction will be automatically canceled ? I really hope that this is true, 800$ is allot of money to lose I hope this get fixed in future
download the bitcoin client or the electrum client.
dump your private keys from blockchain and import. use pywallet to delete the transaction from your wallet.
reopen either bitcoin or electrum.
create a separate wallet at blockchain.info. do not create it under the same account. don't worry you can dispose of this address after you've resent the payment.
send the entire transaction(just sent an even 8 btc you pud)r to the new address you just created, it will show a doublespend but it will go through within a few hours.
now that it has confirmed in this new wallet, you can send the transaction again with the fee and it is all good.
other than the steps i just laid out, your only option is waiting 72 hours, however blockchain.info likes to get stuck in a loop where it keeps trying to send the transactions no matter how many times it gets rejected. its fucking lame.
1 last thing: you should be slapped for storing that much btc in a blockchain account imo.