I suppose it depends on your overall finish plan as well, if you are going for a solid finished colour its less an issue than a translucent or natural finish.
I have seen a couple of threads where the shim in similar materials has been done effectively. Check out the ES-3 thread from Tweaky
http://www.buildyourownguitar.com.au...ght=Tweaky%27s

He did some great work on a similar issue. That way you can make the edge match the bottom binding (after you sand your fillet) and then you are only left with a little Binding patch job at the top. If you can get a hold of some cream/white binding and some acetone you should be able to fill that as well. Dingo Bass did a broken binding repair like this:
http://www.buildyourownguitar.com.au...ead.php?t=5952

all depends on how deep you want to go and how much work you want to do. Potentially if its a colour finish you could just use a wood filler?