If you are creating a campaign and you would like to add one specific person to it, it is now possible by clicking the button that can be found within this campaign:
In this case you can add one person using their LinkedIn profile link, without making a whole new search. Just copy the URL and paste it in the pop up window:
Once you click Send profile link the person will immediately appear in your campaign and you can reach out to them.
Keep in mind that you can add only one person at a time, however you can add multiple people this way.