I don´t think that this is possible. That was a bug from the official servers.
I think the boss would act as if it was rude attacked and just teleport.
You can still try it tho.
Edit in your mob db the dmotion of one mob / mvp to a high value and test it.
dMotion: Damage animation motion, same as aMotion but used to display the "I am hit" animation. Coincidentally, this same value is used to determine how long it is before the mob/player can move again. Endure is dMotion = 0, obviously.
And you might as well edit the mob skill db, to disable the teleport skill of that mob.
Because I´m pretty sure this would result to a rude attack if the value is too high.