Yes you could do it on an affiliate site I guess. I have not checked the coding.
I can tell you that it is a give/take deal. Some times do it and some don’t. Some people are really annoyed by it, some are not. I know it does work and it does increase the signups. The quality of those signups are just a fraction of the quality of a signup that browsed the site for a bit and decided to download from the standard area.