Hi @NotThatJC ,
There wouldn't be a way to accomplish this in the meantime, as there's no functionality for this in any of the systems for making sign up forms, landing pages, or other integrated forms at this time.
You could potentially make your own sign up form with this capability, then work with our Web Services / API Developers team to get it connected to our API. However our general support wouldn't be able to provide any further insight on that process. You'd either need to reach out via the API Developers Support board or their main website.
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