You do need VCDS to do it properly. You need to change the instruments to 'ROW' (Rest of World) Then in the MFD setting, select 'DIGITAL SPEED' You'll also need to change your units back to imperial.
This will give you a big digital speedo in the centre of the DIS and replace the small kph with external temperature. If you need your kph back for driving abroad, just tick 'alt speed display' and it will revert back to standard.