You can enable the deadlocking via a remote but many alarm companies are reluctant to tamper with it as if the alarm becomes active it can lock you in the car. You could probably get it to work with another pair of relays that switch the deadlocking from the alarm lock/unlock signal.

If you get it wrong you can deadlock the car by locking the door from the inside and then you can't get out if you haven't got the key to wind a window down or open the sunroof. I think the boot release is disabled when the car is deadlocked.