Geof Glass and Trevor Bradley sorted out the Marganilia - SCoPE issue. It required a little CSS fix.
So now when you open a forum discussion and activate the annotations function (top right) you will see a yellow bar separating the message and annotation space. If you select some text in a message, then mouse over to the right, click on that yellow bar, or hit your enter key to create an annotation for the selected text. Here's a demo.