There isn't currently a way to add new menu items to the popup. I seem to remember Copy appears if you enable Copy to Clipboard in Edit User Interface.
I may be wrong, but I don't know if it's possible for us to detect when Paste is allowed in the window (which means we couldn't control the menu properly to allow this). The menu/toolbars/etc. is done by us, the HTML ebook viewing window is powered by MS's IE technology, so these types of issues usually arise (and this one problem falls into this category) when there is some difficulty interfacing the two together.
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