I am assuming that you are going to Formats to get a rule that applies to this situation, although this isn't truly a free-standing punctuation mark. Regardless of how you present it, it will not be easily recognizable as a question mark, will it? But I can't think of a solution better than the one you have chosen. Formats suggestion is to use words to name a punctuation mark shown in unusual configuration. If you choose to do that, a tn could explain what that second question mark is.