Fine-grained control over excluded folders

I have a Gradle build that generates some sources. They go into "build/generated-sources" with "build" being the general output directory of the Gradle build. Now the problem is that although "build/generated-sources" is marked as a source folder in the Gradle-generated .iml file, IDEA ignores it because "build" is marked as an excluded folder. Is there a good way to solve this problem? Excluding all siblings of "generated-sources" instead of the parent "build" folder would be fragile. I guess what I'm looking for is a way to exclude "build" but include "build/generated-sources". Does the .iml format support this?

Cheers,

Peter