It’s not quite copy and paste, but KiCommand is developing the ability to specify arbitrary lines/circles/arcs/bezier curves on any layer, using the newdrawing command with input from the command line. You could even read commands from a file. In addition, reading arbitrary fonts is almost ready (I’d say within the next month). There is an electronics symbol font available on the internet. An image of the font is available in this post.
Edit: I captured all the symbols in the font here:
KiCommand will (soon) allow you to place any font glyph as a polygon.