After reading
this thread and with a mod planned for the end of the month I purchased a 3 button keyfob

Swapped the top half of my key over and paired the new remote to the car
End result - middle button now unlocks the boot but not the rest of the car

It will then re-lock the boot after you've closed it so you got to be careful not to leave your keys in there
If you want to do the same read the thread i posted as it may NOT work depending on the year of your car