Sorry it appears I'm incorrect. I have scanned through the Admin and User Guide and cannot seem to find anything that supports adding URL to where I thought it could be added.
The only way to add links is within a campaign by adding a Custom Details page with links in it. If that is sufficient in CIS go to Defintions -> Selection Campaign Definitions -> Custom Detail Pages. You can add a new page with Links and then in the following pane you can place it where you like in the order of panes when editing a campaign.
That's the best I can find. Hope it helps.