Just make sure that after you add the milk you are not boiling the curry. It would be an idea to create the curry base and cook all the ingredients, then just before serving add the milk-coconut extract and warm through, taking care not to boil it.
Other than that I have no idea, I think its just one of those things where you either use it, or you don't. I cannot find any other 'pseudo' coconut milk/cream substitutes other than the one you have already tried (and various substitutes that largely consist of making coconut milk/cream when you don't have any on hand).
The only thing I can think of to lighten it is ensuring that you are using just the coconut milk (some brands labeled coconut milk are more similar to coconut cream). The best way to do this is open a can of coconut milk/cream and setting it aside for a bit to let all the cream rise to the top, skim it off and discard, then use the milk thats left.
Like I said before I think its just one of those things that is really irreplacable. Think of it like this, how many fat people would you see in Thailand? (apart from tourists that is :P) and they would have to have a lower rate of heart disease than us western nations.
Some indian style curries you can get away without the coconut cream. Perhaps you could try stirring through some non/low-fat natural yoghurt just before serving (becareful not to boil), this adds a richness and creaminess to it but of course it lacks the coconut taste, however it does add a pleasant tang to must curries (such as biryani style indian curries). However, when it comes to Thai curries such as red/green/mussaman/panang...coconut milk is such an essential ingredient, if you can't substitute anything for it maybe considering turning it into a stew? Who knows.