Personally, I'll be building a fully anatomic ear clone for my measurements (both pinna and ear canal, in silicone)- we'll see how that goes. Right now I have the outer ear done, making the ear canal is easy (I've done such pouch mold already), next I'll be making the cheek and back of the head, but it's still a lot of time - I'm too busy and the CIEM project is not proceeding as it should anyway.
For IEMs, it seems that the ear canal volume is everything, while the shape does not matter.
For headphones though... without the pinna you will get a "wrong" measurement, but same goes for a different pinna. I'm pretty sure now this is all due to directional properties of the outer ear, somewhat due to ear canal volume and total trapped air volume, and not the ear canal shape itself.