While performing inspections, you often need to reference other materials. Other source code files, Requirements and Design documents, etc. Currently Collaborator has no way to include these as...
Interesting, when you upload files a review using the client, the last step is to include any reference files - but you are right, these are mixed in with the rest of the files so there is no good way to distinguish. I would be for putting in a separate "reference files" section which would clearly identify files that are only for reference, and not part of the review. You could have a separate "upload" button to easily include files in this section, and files uploaded to this section would not contribute towards the LOC and other auto-generated review metrics reported by Collaborator.