This plugin allows you to set SOPA blackout dates for your WordPress website. SEO friendly plus easy options to configure how often it's shown.
Q. Are the redirects used SEO friendly? A. Yes, 307 status headers are sent with the redirects, which are temporary and SEO friendly.
Q. Can I see an example of what the SOPA page looks like? A. You bet! Take a look here for a demo http://www.wpsopaplugin.com/stop-sopa/