Ben, one thing you can do is hinge cut a few trees around the edge but not enough to block travel lanes. I'm talking about an irregular edge where some hinged trees will extend out into the field and others may lay along the edge of the woods. In our area, you should get some honeysuckle growing up on the hinged trees at some places, which adds to the effect. You should also get some blackberry briers and saplings coming up in the tops. This isn't what I would call a typical feathered edge, but it is effective in a lot of ways. As the tree tops eventually die you will be left with a soft edge of briers, honeysuckle and saplings.