What you can do is setup an automated trade system in NinjaTrader and instead of using NinjaTrader trade management software, you send an email out to ZeroLine Trader to place the trade for you, and then ZeroLine Trader sends the order to Interactive Brokers. Using the Perl script I've written, and with a little bit of coding, this is a very simple setup and gives you a fully functional automated trade system for Ninjatrader through Interactive Brokers without the extra cost of having to own Ninjatrader or pay the extra cost for placing each trade. Having the automated trade system run directly through Ninjatrader to Interactive Brokers will be slightly faster and may be slightly easier to setup; however, using ZeroLine Trader as a middleman to save on the extra fee's may be worth it.
Here are the Downloads you will need-
Charting and Trading Platform