As far as I know you need a capsule to do it. If you use more than one capsule in your hub it can be placed just about anywhere on your hub. Most people add the capsule at the bottom of the hub. The idea is you don't want people clicking away until they have read the hub.
I agree with this thinking, if you can't keep your readers attention until the end of your hub you might as well just not write it. The only link I have on a hub is on the bottom just for this reason.