Have iPhone NOT connect to car Bluetooth unless I am in the car

Here is my use case.

Oftentimes, I am in my house doing a workout on the bicycle, and my wife will get in the car to go somewhere. My watch asks me to pause my workout (this is easy enough to dismiss) but the next part is more frustrating.

The iPhone connects to the cars Bluetooth, and the audio moves from my AirPods to the car for about a minute, until she backs out of the garage and drives off.

The same will happen if she comes home. This also happens if I am listening to audio through the HomePods, which can be more annoying because it just stops (no notification of paused workout as I am not working out).

I want to run an automation that only connects to Bluetooth when my phone is in the car. I thought of using an NFC tag, or a beacon. But I don’t see the way to do this.

Any thoughts?

This was the subject of an askatp question a few weeks ago. As I recall, no good solutions were provided in that discussion. It seems like a common frustration with no good solution.