no worries Mindis looks like the factory forgot to drill this hole.
Have you got a long drill bit about 4mm diameter ? Not sure what the distance is to the volume pot cavity, you could try a standard 4mm drill and put tighten it close to the end of the bit to give maximum bit length. I would say you need a long drill bit like this
http://www.bunnings.com.au/sutton-to...l-bit_p6351998
draw in pencil a line that is about centre of jack hole to centre of volume pot cavity and angle the drill flat so it comes out about centre depth of the volume pot cavity to lower the risk of drilling out of the top or bottom of the body. This way to can line up the drill bit angle