Three choices, build higher, snip or leave them alone.
If you can build more, put something for them to grow up another 6 feet or so. you'll get more hops.
You could snip off the tip of the main bine. This will cause more side arms to grow, but most liklely one will try to become the dominate bine and continue the growth up. So there is a chance you will be hurting yourself because its putting its energy into the upward growth instead of making cones.
You could ignore it. It will realize it can't go up any further, stop growing and worry about making cones. Of course this is the easiest.