Ok have done some handbook delving and it's not that simple as it depends on what spec car you have as to whether or not you can enable/disable "boot only" unlock ...
If you have "Multi-function display" you can't do it (page 25), however if you have “Reconfigurable multifunction display” (page 30) you can.
Page 30 – 31
Various waffle about “Reconfigurable multi-function display - you'll need to read this!
Independent boot unlocking (Indep. Boot)
With this function it is possible to unlock the boot independently from doors.
When the function is enabled, the trunk opens by pressing `on the electronic key, or by acting on the lever located under the left back seat (refer to “Boot” paragraph in this chapter).
To activate independent boot function (ON) or deactivate it (OFF), proceed as follows:
- briefly press button MENU : ON or OFF (according to previous setting) will flash on the display;
- press button + or – to select the required language;
- briefly press button MENU to go back to the menu screen or press the button for long to go back to the standard screen.