Couldn't you write a script for btc-e to do this automatically? Whenever a BTC payment is received @ btc-e the script would activate selling bitcoins for usd or buying btc when a purchase is made. Sounds pretty simple to me but I'm no programer. This could also work with cryptsy usd trading activated.
A script could also be written to track btc-e/cryptsy live price feed.
Btc-e.com would have to write the script to convert automatically inside their site, for the Btc-e.com live price feed this is possible for us to do or they already have one.
We are trying to find a solution that already exists, I think coinbase and bitpay will only pay to checking account and not leave the money in the USD wallet so you can buy bitcoin again.
OKPAY are doing this but their rate is 4% which is high.