Running an Erg Workout from Garmin Head unit during a Group Ride?

Is this possible? I tried a few combinations of pairing configurations but couldn’t get it to work. Can you even enter erg mode if you’re not running an in-game workout but doing a ride instead?

If it matters, head unit is an Edge 840. If anyone has step-by-step instructions on how to run a garmin-connect created workout to do an Erg-based workout during a Zwift group ride, it would be much appreciated! Use-case is to run these during rubberbanded group rides.

I run Trainerday workouts from my phone in ERG mode. You just connect Zwift to your trainer as the power source, but make sure it isnt connected as controllable. Has worked great for me, just make sure the group ride doesnt have an advertised pace that your workout may take you over.

Thanks. As mentioned, I’d run these during rubber-banded rides, meaning that no matter what power you’re doing, you’ll stay with everybody else.