I know, it's such a waste to do that. I have read that you can freeze it, but I've never tried it myself - perhaps you can be our guinea pig?
I have a mincer, so I grate mine and then dry it slowly in the oven to preserve it. If you set the oven to ON, and no higher, it will work just like a food dehydrator. It will take a few hours and you have to make thin layers of coconut on the oven pans otherwise it will go rank.
Another option is to make coconut milk - I know you can freeze that too. First, you grate the meat with either a grater or a mincer. Then you combine it with warm water for a while, then you press it out with whatever you have handy. I use my juicer - it extracts the liquid and spits out the pulp, leaving one with beautiful fresh creamy coconut milk. If you don't have a juicer, press, or other device, you can simply squeeze it out by balling it into your fist - that's how the primitives do it!