I'm not sure if that cooler would be sufficient to cool a 470 though as they do run a bit hotter than a 4870.
It's not about how hot it runs - that's affected by the cooler mounted and such, and the GTX470 stock cooler is more effective than the 4870's. It's about how much heat energy needs to be dissipated. This is where the card's TDP comes into play. The 4870 1GB has a 206W TDP while the GTX470 has a 232W TDP. So while the GTX470 'runs cooler', it actually requires more heat to be dissipated.
(Figures taken from TPU's GTX470 review)
That epoxy thing gave me an idea.
I recall while at work a colleague was using some form of metal based epoxy that set so hard it was almost as strong as proper metal. If one could procure this stuff and build extra length to the arms if both sides if the cooler retention bracket. You could drill this stuff and everything. Shouldn't be more than a few quid to buy.