As i see it, the “real” method would be to create a custom shader (.usf file) to do what I want. But the documentation lacks a lot of things there:
https://docs.unrealengine.com/latest/INT/Programming/Rendering/ShaderDevelopment/index.html
Where do I have to put the .usf files to? Dragging them into the editor results in “unknown file format”. Is there a default folder for shaders? Lots of information is missing there at the moment.