Yes, that is correct. If you do this be sure you do not bridge out of the ground “lanes” under the chip. This probably means milling your heatsink.
Another way to do this without drilling the holes is to use a Berquist (or similar) double-sided sticky, electrically insulating, thermally conductive pad. Something like this:
http://www.digikey.com/product-detail/en/BP100-0.008-00-1010/BER159-ND/307781
I’ve had good luck with this. You can just cover the entire back of the board and pop a surplus Duron or other heatsink on that’s the approximate size you need.