Hello,
I have proven experience of doing co-reg script that optins the same subscriber to multiple subscriber lists (no matter where the auto responder is, can be custom build, aweber, mailchimp or any other.). When it comes to well known providers like aweber, you can't use server IP.
I can fix your co-reg thing and can change server IP to local subscriber IP address.
More information needed, Please talk first.
Regards,