Although it looks untidy you could do what I've done with that fifth internal port. Before you put the side back on the PC connect a USB cable to the internal port and find a suitable orifice somewhere at the back of the PC to feed the wire through. I'm using it for a small Brother label printer that sits on top of the tower so it only needed a short bit of wire.
Make sure that the hole in the case hasn't got any rough edges or again do what I did - stick a bit of insulating tape round the edges of the hole. All that 'cos I was to mean to buy a USB hub!
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.