Instead of trading, the EA must send the trades to Zorro, which in turn sends them to Oanda. For sending the trades to Zorro, the EA must poll the ZorroRequest function similar to the Zorro EA, and return the position parameters f.i. as a response on CMD_BCOMMAND codes. That's the basic principle. It is possible, but not a trivial task, because the MT4 bridge is designed for sending trades in the other direction.