How do I use Handoff in the middle of a call? I received a call today, and the Handoff box popped up on my screen as usual. I took the call on my phone and the box disappeared.

Then, partway through the call, I wanted to "hand off" the call back to my computer. But I couldn't figure out how to do it, and the Apple help page wasn't very clear.

How can I take a call on my iPhone and then pass it to my MacBook? I'm running iOS 9 on an iPhone 6S, and OS X El Capitan on a MacBook Pro retina -- so I know my hardware is capable of it.
As of iOS 9.2, you can't do this in the middle of a call.

To talk using a different device, you must end the call and recall using the second device.