В инете пишут что-то такое
<script type='text/javascript'>
function addLink() {
if (
window.getSelection().containsNode(
document.getElementsByClassName('entry-content')[0], true)) {
var body_element = document.getElementsByTagName('body')[0];
var selection;
selection = window.getSelection();
var oldselection = selection
var pagelink = "Ваша ссылка"; //Change this if you like
var copy_text = selection + pagelink;
var new_div = document.createElement('div');
new_div.style.left='-99999px';
new_div.style.position='absolute';
body_element.appendChild(new_div );
new_div.innerHTML = copy_text ;
selection.selectAllChildren(new_div );
window.setTimeout(function() {
body_element.removeChild(new_div );
},0);
}
}
document.oncopy = addLink;
</script>