Real-time forward of data to another application

Hi I am looking for a network sniffer tool that can pick specific packets generated by one application and forward them to another application in real-time (pass through or forward.The application that generates the data is a point of sales (POS)system serving 30 cash registers. The application that need the data is a queue management system that predicts how many checkout lanes need to be open in real-time. I need this for a proof of concept for in store trials. Retailers don't like writing POS interfaces to applications that they are testing and have not decided to purchase.