Ok, so there's no way to safely spoof the ip address of a curl request, but I found a non-safe way, it depends on the server script receiving the request, but it worked for me to trick the API I was making the request to:
curl_setopt( $ch, CURLOPT_HTTPHEADER, array("REMOTE_ADDR: $ip", "HTTP_X_FORWARDED_FOR: $ip"));
This won't always work, but in this case it worked for me.
Thanks everyone for the help!
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