By far the harder part is attaching the line to the streamer! Is that what you were really interested in finding out?
Competition streamers are only allowed to have one line attachments, but no one says that you can't use a yoke for sport streamers. One way to do this is with an "M" or "W" attachment. As the name implies, first you attach the center of your line to the center of one edge of the streamer. Then you stretch each half of the line upward at an angle toward each outer edge and bond those diagonals to the streamer. Finally you extend the rest of the line down toward the end along each side edge and bond it along those edges. Then you take the two free ends and tie them to your swivel. You lay tape over the sections of the lines to bond them to the streamer. What type of tape you use depends upon what material the streamer is made of. You want to use something that will adhere well and will not pull off very easily, if you can even pull it off at all. Also, you don't want to leave any sticky surfaces exposed because they will cause parts of your streamer to stick together when it is folded up.
With a little bit of imagination, you can probably come up with variations of the "M" (such as the "Box"). The principle is that you are trying to bond a good length of line to the end of the streamer in such a way that it will not be easy to pull it off and so that it will not tear the streamer material when tension is applied to it.