Getting ChatGPT app to work with a trigger phrase

Ive enjoyed using the iOS chatgpt app using voice input. The problem is that there is no trigger when using the app, unlike Siri, Hey Google, Alexa, etc. Has anyone worked around this? I noted a flood of ioS apps that wrap their functionality around the GPT API, but I don’t want to pay for ChatGPT+ and then also pay an app developer. I just want to replace the outdated chat technology used by hardware voice assistants. Really love the iOS chatgpt app, but without a trigger phrase, I cannot see this being in wide use in the home. I also searched this forum for previous questions, but couldn’t see anything close. Thanks for your suggestions.