So you want to be able to train in Teams/Zoom, have someone muted, and don't want mute beeps? Great!
Instead of pairing a secondary mic to the base for training, let's try our favorite feature: UniBase!
Get yourself into phone mode, then press and hold the computer button on the base until that light illuminates. This will make it so you can merge the computer and desk phone calls together. Once done, call the other person on their desk phone and have them answer with the headset and then mute from the phone.
Now the trainee can listen in, not be heard by the Customer, and also not get those beeps!