I was thinking the opposite, keep him up top but encourage him to attack. India will surely turn to spin early, and I'd be tempted to tell McCullum to hit anything that gets in his area. Not reckless, all out attack, but enough to disrupt the spinners and force Dhoni to turn to pace again or to set defensive fields.
It might address the point that's bugged me about NZ, first in WI and now here in India - their batting run rate has generally been VERY slow. All about survival and not much about working out how to get off strike or how to change the bowlers line and length.