Being involved with many things "Google" the past 8+ years, I would highly advise against this method of SEO.
Just as you pointed out, it will get you banned by Google. It might take a little while for the Google Bot to catch on to every site doing it, but once you are caught, into the Google blackhole you go and it almost takes an act of God to get out of that blackhole once banned, especially for something like this.
If you need some SEO help for your client, contact me off forum and I'd be glad to help. People who know me are aware of how well I can get people indexed with Google (and other search engines) and not by using blackhat or unethical methods as your client seems to want you doing.