Did you thought of using other exchange that could provide the service your asking for?
Yes, couldnt find any Exchange with many altcoins and usd. Or any way of immediate Transfer of USD to BTC and BTC to USD.
You can actually trade your coins for USDT at Bittrex. It is a token supposed backed by 1 USD.
1 Tether (USDT) is worth 1 dollar, so you can for example, sell 1 BTC for 4350 USDT and rebuy when the price goes down without needing to transfer money between your bank account and the exchange.
But I would be careful, they seem to be shady at the moment. Check the links:
https[Suspicious link removed]d/status/904867721652797440
https://www.reddit.com/r/btc/comments/6y4p49/tether_has_created_a_total_of_70_million_in_new/Yeah i heard about Tether already, definitely not a good solution atm, thanks anyway