Well, I decided to try this process.
First I've done what I said here some time ago. Took a little part of both compounds, mixed together and let it cure on my earshell. It never firmed up.
I contacted the vendor and the answer was: For some reason it will never firm up if you mix a little part. You really have to mix the whole thing together.
So, I want to make one thing clear: The material is VERY consistent. The idea of it slipping inside your ear and getting to your eardrum is nonsense. It will never happen. It is so consistent that even if you try to push the thing in, pressure won't allow it to go further. The only way it can go to your eardrum is if you mold it pointy and insert it into your earcanal like a retard.
My first earmold is ready, it is a very hard rubber after cured. Only 15 minutes to cure.
The little part I tried before never cured, it is still a putty, can be molded and ripped. But when I mixed the whole thing up, it went fine as it should.