Its probably worth mentioning I have a rear AUX input, so it goes straight down the back... However if it was a front port, you could drill a hole in the fascia to accomodate it, then do the same thing. Also, I'd reccomend getting a 1.5metre cable for this, just so you have enough cable!

Right Ill do this in steps for you, should make it easier!

1. Remove headunit/ drill hole in fascia.
2. Remove plastic centre console trim (see Punto Guides, its 4 Torx screws) unclipping the cigarette lighter before pulling it off, then remove the trim that holds the city/heated rear screen buttons, but dont disconnect the buttons.
3. open the glovebox and feed the AUX cable down the back of the HU hole and to the left. If you lean into the passengers footwell you'll be able to see it and guide it correctly (expect grazed knuckles and swearing here), then feed it back through towards and around where the city button would be
4.Refit city button panel
5. now you've got the cable there, just pull it through and find a place to run it down where it wont get in the way of any knobs or buttons. tape it in place if you need to, i managed to squeeze mine between two knobs and it sat there nicely.
6. If you look at the centre console, there's a hole just at the top of the cubbyhole where the cupholders are. Feed the wire through there and refit the centre console. It should now be sat in there looking more out of the way!
7.Get a cuppa and admire your work.

This was edited from memory, so may need tweeking. please comment as neccessary!