Hey you know, if you create two text widgets, you can make things easy on yourself. Do the ribbon now so your readers get an idea you're onto something new, and set up the blackout text but hide it by dragging the widget to the very bottom of the page, in the "inactive widgets" section of the widgets page. That way, you can simply switch them out on Thursday morning, and remove the blackout Thursday evening.
Right now I have this text in my inactive widget:
<div align="center" style="position:fixed;width:100%;height:100%;top:0;right:0;z-index:100000;background-color:#000;-moz-opacity:0.8;opacity:.80;filter:alpha(opacity=80);font-size:800%;font-weight:bold;padding-top:300px;"><a href="http://americancensorship.org/">SAVE THE INTERNET <br />Stop SOPA</a></div></p>
<p><div>This site has been taken down in protest of bills currently being considered in the US House and Senate. Called <a href="http://thomas.loc.gov/cgi-bin/bdquery/z?d112:h.r.3261:">SOPA</a> and <a href="http://en.wikipedia.org/wiki/PROTECT_IP_Act">PIPA</a>,<br />
these bills threaten to destroy the Internet as we know it.</p>
<p>If either one passes, your favorite sites could disappear forever.</p>
<p><p class="act">ACT NOW.</p></p>
<p><a href="http://americancensorship.org/modal/call-form-moz.html">CALL YOUR SENATOR AND ASK THEM TO VOTE "NO" FOR PIPA</a></p>
<p><a href="https://github.com/SaraJo/SOPA-PIPA-Protest-Page">JOIN US</a></p>
You could add the video (using VodPod) to the above, at least in theory. Hope that helps! And thanks for even wanting to support the fight.