Just read this on reddit.
Aparently the Templar will not detain you in the bubble if you are out of his line of sight and not looking at him. Several people tried it and confirmed it.
So if you aren't just gonna cheese him off the cliff, don't look at him and stay out of his sight line. The only person to be detained will be the relic holder who suppers him.
Also suppose to work on atheon hard mode.