So, I fixed it by importing it as an accessory, than transferring the skin weights as a skin tight t-shirt. Than I hide the faces of the original mesh that where overlapping and weren't needed. And when exporting I have to make sure to select the Delete hidden mesh option. 
All the functions still work, as long as i don't adjust the skin color. But for me this is fine for now. 
The morph option would have been a cleaner solution, with future use in mind, but I couldn't get the objKey working when trying to create the morph object.
So since I need this to work quick in unity for a deadline, this is perfect for now. 
In the future I may try to get the morph solution Vidi suggested working, but for now my problem is solved. 
Danke schön @Vidi