Problems animating from a cone shape to flat mesh surfaces

Hi,

I'm fairly new to blender and i have an animation project where i'm 
supposed to show the process a 3d cone unwrapping itself into two flat 
shapes, a triangle with a curved base and a circle. I've been playing 
around with animating lattices and shape keys but just not getting a 
real satisfying result. Is there any existing tutorials that 
demonstates this or something similar or has anybody attempted this 
before that could give me a detailed step by step. I would even accept 
a scene file that i could modify.