Something very similar to a worm trench is the worm tower.
The theory behind a worm tower it that you can feed the worms from above the ground via a tube that sticks out of the ground that is also buried below the surface. The theory is that the worms will come to the tower to feed.
My overall opinion is that this is a great way to encourage native worms to come hang out in your garden but I would NEVER introduce red wigglers into this system. Why? They are not garden worms, they are manure and bin worms, best suited for ideal environments and if you cannot provide that ideal environment you will be sending them on a suicide mission. Just my thoughts.
Here is a video of a worm tower:
One thing I do not understand, if someone has had a worm tower, please help me: How do you get the castings out of the tower? Do you eventually have to move the tower and empty it out every now and then? It would seem to me that it would fill up after some time.