Scenario, shortish par 4 (320 yds or so), OB fence line down the left side, but about two feet of sparse bushes before you get to the OB line. A drive comes to rest in the bushes but not OB. Ball is deemed unplayable, players measures two club lengths from the spot of his ball (no nearer the hole), drops, proceeds to hit his next shot to 2', makes the putt for par.

My question is, for an unplayable, do you have to keep the point of where the ball was deemed unplayable between you and the hole, and if yes, and this cannot happen based on the design of the hole, does the player have to go back to where the last shot was played from?