I've done this in the past. The way I did it was just to send rosstalk commands to the GPI card. Here is one of my sample tasks:
rosstalk.sendMessage(params.getValue("GPICard_IP",0), params.getValue("GPICard_Port",0), 'GPI 17:ON');
I had parameters to hold my IP and Port, but you could just do:
rosstalk.sendMessage("10.2.3.4", 7788, 'GPI 17:ON');
It's been a while since I did this, and I no longer have the GPIO card, but it seems to me its IP address is listed in one of the tabs of the config tab.
You could also do it with a Visual Logic block (Send TCP Messages (String)), like this:

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