well, even if you can find the space around the chip to put it on (and looking at some piccys there doesnt seem to be w whole lot thanks to some large capacitors), doing it might well be a pain.
two methods I can guess at: gluing the thing on with thermal adhesive (artic silver do some), which would work provided the heatsink isnt too heavy that it threatens to pull the northbridge off the motherboard. yes the adhesive does seem to be stronger than the way the chip is put on the board and this happens quite often when people try to rip off video card 'sinks that have been put on this way. Using 100% thermal epoxy, the sink is not going to be seperated from the chip in any hurry. Using a 50:50 or 60:40 mix of adhesive and normal thermal paste, well it's still a case of trying to figure out what mix to use that will allow you to take the 'sink off the chip while not allowing it to fall off, and you wont be getting much in the way of second tries.
only other way I can think of is to drill holes through the 'sink, so that you can put a bolt through the heatsink and out through the holes in the motherboard (the holes currently used for that purpose). Even still, you'd want some fairly large washers at the back to spread the weight instead of a little screwhead, and there might be little components that could be in the way of those or worse something for the washer to short-circuit.
Seems more than a little OTT to me, and I wouldnt be so confident that even if you made it significantly cooler you'd get any better overclocks.