Is it possibile to manually wire a displayport cable?
I can't say for certain that it's impossible, but at the very least it would be very very difficult to wire by hand.  Modern video cables like HDMI and displayport need high quality connections and wire, and I doubt you would be able to get the quality needed by hand.

The nice thing about digital video cables is that you'll know if it works - it either works, or doesn't work (or sometimes works in which case you'll either see nothing or a scrambled display).  There's should be no loss of picture quality.  

So you can try it...but I have a feeling enlarging the hole would be your best bet.  Displayport connectors are still fairly small so the hole won't be too big.  Or you can do it the right way with a big hole and a faceplate.  You can get faceplates that just have a hole in the center to pass a wire through but are actually two pieces that snap together so you don't have to remove the connector.