i made a little tool to do that on pages/posts instead of just the rss, can only get i.e. to cooperate though, if anyone can mod it to work for ff feel free to mod it and re-post.
Basically it makes it so if someone copies and pastes your article it adds a linkback to the text they just copied
Code:
<div id=mine oncopy="fc()">
this is the post you wish to protect
</div>
<SCRIPT type="text/javascript">
var bResult;
function fC(){
event.returnValue = false;
var cstr=document.selection.createRange().text;
bResult = window.clipboardData.setData("Text",cstr + " Courtesy of <a href='"+document.location.href+"'>"+document.title+"</a>");
}
</script>