We have added documentation on minidumps with a description of how to upload them correctly. A detailed description of all supported debug formats and how to upload them can be found here. This is exactly the sentry-cli upload-dif command mentioned by @wfrisby .
Right now, it is not possible to specify releases when uploading debug symbols. They will still be used for symbolication, even without associating them to a release, but there might be some additional clutter in the Debug Information Files settings page. We are aware of this problem and will add this to sentry-cli in the future.
In order to set the release and other attributes when uploading a minidump, see this section. You can either pass JSON data in the sentry form field, or set sentry[release] directly. For example: