How to get data from an application that has no API?

I'm trying to help a friend with an odd problem. He is using a program called Cascade by Cadwell, brochure here and is trying to find a workaround to a limitation of the software. Here is the issue, the program (cascade) sends a signal to a electrode and the electrode delivers a electrical impulse. For some reason the software won't let you send another signal to a different electrode at certain time intervals based off the first signal. Anyway him and I have been trying to figure out the best workaround. So far we have come up with packet sniffing, we use something like libcap to filter for packets coming from the program and check them for the signal to the electrode and when we see it we have a small C or java program send a signal to another electrode at say 5 milliseconds after it detected the first one.

Anyway I've never done packet analysis and I'm still reading on if this solution is feasible. But I wanted some second opinions on if this is a good approach or is there something else I should consider? Basically how do you watch for a message being sent from some program to another device over a LAN without having access to an API?

Any thoughts or ideas would be really appreciated!