Automatically add a participant to ad hoc meetings.

Is this person the same person all the time?  Is this person’s Zoom account on the same organizational account as yours, and licensed?

I would probably recommend using Scheduling Privilege between you and the other person.  They would have the ability to see your meetings in their Zoom client, and would join as co-host. 

See this Zoom Support article for details. It's a little technical, but once you get it done, it’s easy:

https://support.zoom.us/hc/en-us/articles/201362803-Scheduling-privilege