This is in the same vein as Answering questions with a comment - is this usual? Oftentimes I am looking for unanswered questions to try my hand at. Sometimes I find one I can answer, but then find the answer was posted in the comment and the post was subsequently abandoned by all involved. Other times I don't initially know the answer, but the commented answer appears by all means to be correct. Should I post an answer that simply rewords the answer provided in the comment? I'd like to do so so that the post has an answer provided, and to increase my rep, but I also don't want to appear to be claiming other's knowledge as my own.
Imho, it is fair to repost the comment as an answer if a reasonable amount of time, i.e. a week, has passed and the commenter doesn't seem interested in posting an answer. This (+ at least one upvote) is the only way to get the question recognized as answered.
Alternatively, you can try to encourage the commenter to post his/her comment as an answer. Sometimes it works. Other times, you can certainly use their information to post an answer without feeling bad.