With gin-cli version 1.11 Build 001459 (103e923) with git: 2.30.0 and git-annex: 8.20201129-geb388e6 it is possible to unlock files without having the content downloaded via gin get-content. In that case the file link is replaced with a file containing the annex object link, e.g. '/annex/objects/MD5-11111111111--a9f5d017dabfffe571070a3157de37d9'.
I would have expected the gin-cli to either raise a warning that get-content needs to performed first or to automatically run get-content on the specific file prior to unlocking.