Most commonly, the simplest solutions are the best. This is my automatic tailgate mod, using the factory remote key fob.
Also, To unlock it from outside, just press “Trunk” Button on the remote control (key-fob) – or use the key. We’ve already got gas springs to dampen the opening action, so all you need is a coil spring or elastic tie down large enough to lift the lid against the friction of the gas springs.
Undo the trunk fuse flap thinger. Attached one end to the metal that the flap thinger secures to. Wrap the elastic around the metal tab on the trunk arm. Attached the other end to the same place as the first end. Then close your trunk and test. You can use varying lengths of elastic to adjust the speed of the rising of the trunk. You can also mount the hooks other places for the same effect.
Maybe this sounds complicated, but it’s not at all. It will be much clearer to you when you look at a few DIY videos made by Saab owners who have done this little modification: