Yes, 240s and 260 do have electric trunk openers, located in the glove box, as everyone else has said. I recently installed one found at a parts yard into my 81, so I'll try to hit the important parts.

There are 2 different styles of trunk locks on 240s, pre 86 models (or 81 if not in the US) and 86 and later models, and each has its own type of motor. The 740/760 models I saw all had the exact same motor and lock as the post 86 240s, which is the rectangular chrome looking one, as opposed to the little round circle type. Any lock can have a motor added to it, all you have to do is snag the motor and the little arm that connects it to the lock. The holes to mount the motor to are already in the trunk/boot, and after pulling one out of a car it'll be easy to get one in. I had no real problems putting my older style one in, there are some pictures in the Bently manual somewhere that may be helpful.

The button for the glovebox is simple to install, its just a push button thing, but it looks a lot better if you grab the little metal plate with the picture of the open trunk on it. Simple two wire hookup on the back, one to the fusebox if I remember, and one to the motor (black). The power for the motor is the green wire, and I swiped the setup from the wrecked car that split the power at the trunk light, so no need to run an extra wire from the battery or anything.

Overall its pretty simple, only a few wires involved, and mounting is easy. Good luck finding one at a junkyard, that was the hardest part for me.

Hope this helps, sorry for the length.