how install aux/usb in your midconsole

[Mascotte-NL]

hi everyone 
i have bmw 420i it has also two usb connections 
one in the dashboard and the other one in the
midconsole. i have seen other bmw they have an 
extra connection in the midconsole the AUX/USB
connection. is it posiable to retrofit that AUX/USB 
connection. has every radio/hd unit that AUX connection 
on the backside?
Is there anyone who did this retrofit and is it an easy
or difficult DIY

thanks for any reply