I've seen it said in some Wikis that one can activate the gate lever from the outside. I just took my best shot yet at doing so--even trying Telekinesis, squatting down in Sneak, etc. Can't get at it.

Is this action impossible, and the Wiki information is just wrong?

You can using tcl through the console. That's the only way I've ever seen to do it.

There was a way to use the unrelenting force shout on a follower to shout them through the gate and then you could ask them to pull the lever. People said it worked i never tried it though so I'm not sure.