Hi, Michael Guest. Actually, I'm also not sure how to add a CC license to the uploaded PDF files. But I find some files on the RG would claim a CC-BY-NC-ND license. Do you have any solution now?
I also faced same problem. During uploading my technical report I was looking for this CCBY option but it did not appear. I don't know why. Luckily, I inserted CCBY lisence in my document before uploading it into RG.