Does borg offer a way of doing so?
I am unaware of this capability within borgbackup.
You are correct that there is a theoretical possibility/likelihood the data is readable because it isn't actually encrypted -- simply hashed for integrity verification.
This does not mean the application has a mechanism for doing so, which is what your question is actually asking. The documentation does not indicate anything like this functionality.
I assume you are interested in accessing the data regardless if borgbackup itself actually has the functionality. If yes, read on.
"That is not possible" is a valid answer --
This doesn't mean you are out of luck reading the data, but you are probably not going to use borgbackup tools if you succeed. I would suggest applying standard search, text processing, expression matching, etc. tactics to the data on disk that borgbackup has archived, and see what you can come up with.