I managed to get progress on this front by leveraging CppSourceSet 3, which is part of the ‘cpp’ plugin for Gradle. This allows for elegantly expressing multiple header file import locations.
Hence, we can simply do:
headers.srcDirs = ["/usr/local/include/torch/csrc/api/include/", "/usr/local/include/torch/"]

This manages to resolve the headers issue.
I cannot confirm if it completely works because I am since running into a C++11 ABI issue, but once I resolve that (which I believe is caused by another problem) I will look back and confirm that it is solved.