My problems are solved thanks to an answer in the comments. I also would like to provide official recognition by accepting this answer, but I can't.
Unfortunately, there is nothing much you can do except asking the user if he is willing to provide the comment as an answer so that you can upvote and accept it. In the end, it is the user's decision.
Sometimes, especially with high-reputation users, they might suggest you write the answer yourself using the solution in their comments. That is not so unusual and a good way for you to get some points. So don't be shy.