Ability to link Contact to a Campaign

I would like the ability to link or attach an existing Contact to a Campain. Currentyl, you can only create a new contact within a campaign, but not existing ones.

For example, I may want to re-assign a group of clients to a new advisor. So, I create a Campaign called "Clients to Reassing to John", then I add all my clients to that Campaign.

Then, as we change the agent on a client to John, we remove that contact from the Campagin.

If there is another way process this workflow, I am open to ideas.

thanks