I've shared this work-around on facebook's "Lightwavers are Everywhere" users group. I needed an overview of 8 different Substance Designer materials each with it's own bakes (roughness, basecolor, normals, and so on) I don't really understand why this worked but it does at some point. Now I have control over specific maps on specific instances. Would be nice if someone can improve this work-around.
This solution breaks if the seed is not 0
and also doesn't work any more if i have 9 or 10 instances.
For my purposes it works ok.
Video:
https://youtu.be/t7k-dmHEJWU
Facebook Discussion: https://www.facebook.com/groups/lightwiki/permalink/1081761798596485/