Adding a third party on a FaceTime audio call

Using FaceTime to make phone calls. I want to add a third party to a call I initiate.

It appears that I have to pick up my iPhone and do it there, but that kicks off the FaceTime call, so I can't listen through my computer. (I can record the call using FaceTime.)

Am I missing something? Is there a way to add a third party to a FaceTime audio call?