Aweber.com implementation of "Sign Up Co-Registration" concept?

[reg.copperman]

In Level 1 (Starter Kit) I found the "Sign Up Co-Registration" templates.

The Integration Point simply consists of one text line on a registration form:

"Yes, also include a FREE subscription to {co-reg newsletter name}."

Details here... (http://multimedia.integrationmarketing.com/classes/starterkit/templates/web/versionA/sign%20up%20co-reg.htm)

I was wondering if anybody knows a technical solution for implementing this technique in case the co-reg newsletter is hosted at aweber.com.

And - most importantly - this technical solution should comply with aweber's terms and conditions.

So - any experience with this? Or any ideas?

Thanks for any comment :)