Don't think you can as Bethesda has changed it so it has to fully load in before it takes damage all because of auto axe users was abusing it, they tried the 2nd patch and did stop some but guessing their 3rd time was the charm.
what i normally do is hide behind a piller and OPK and aim for the back till the shield is down, then turn OPK off and vats the main body to kill it. this is the quickest way to take it down....
also have you noticed the hit boxes for the snake is worse as when you aim for the right eye using vats works then just....stops.
What i do is get close as possible and soon it pokes its head out.... Jump and vats thar eye and i get it killed before the tail spawns in.
