"However, it was unanswered, and their only option to bring attention to the question seems to be to do the wrong thing, and ask it again"
The correct thing is to ask a new question. If a question is technically a duplicate but original has no answers, there is nothing wrong with asking it again.
Do so by making a new post (not a commenting or writing in the answer section), and ideally mentioning the original post with a link to it, so as to acknowledge it and show research efforts.
It is not consideres a duplicate nor a wrong action, and except for mods you can't even close vote as duplicate of a question with no answers, or if any answers only have no upvotes or negative score.
To answer your question directly, to bump an old question a user can:
- As Glorfindel mentions add a bounty if you have enough rep to spare.
- Improve the answer by fixing any mistakes or adding proper tags.
- Add new details or additional information that can help solve the issue, if those don't conflict with the meaning of the original author.