I had a cheap pair of airplane earbuds lying around so I decided to experiment with it by taking the earbuds apart and putting it into a semi-custom IEM housing.
I've Uploaded My Own Right and Left Ear IEM's as an example
To make your own, here are the steps:
Download williamyeny's general iem template here:
Take a picture of your ear and head to Smoothie 3D : https://www.smoothie-3d.com
Create a shape for your IEM
Extract the model and edit it in any software (I used Tinkercad to show that it's stupidly easy).
Remove the original casing from your earbuds of choice
Insert and put the printed IEM together