“In a webmaster hangout on Google+ this morning, Google’s John Mueller basically said there is no good way to redirect a web site that has a penalty to a new web site without a penalty and not risk the new web site being penalised.
It gets very close to cloaking, where you are saying users see this behavior and search engines see something completely different. And that is something I’d try to avoid. It goes against the webmaster guidelines. So maybe a pop up like you have it now is your best approach at the moment.”