If you want, you can theoretically manage trades even with a NFA plugin. The plugin must then keep track of trades and synchronize them with open orders and position sizes. Since this would reqiure a lot programming, we do not mention it in the manual. I also know no plugin that would do that. NFA plugins normally don't use BrokerTrade at all.

Simply return all information that you easily get. Return the fill amount when you get it from the order, otherwise return NAY.