@KronoS: The answer should be self-contained. Links should only provide further information. If that can't be achieved, for whatever reason, explain what to expect from following the link.

@Dennis: I fully appreciate the problematic situation. I just always felt like the "no registration" part was an important cornerstone of the "openness" of StackExchange. Personally, I wouldn't feel well about sacrificing it. A different solution to the issue would be interesting. Sadly, I can't offer one at this point in time :(

You already found the solution.

I usually have the reverse issue when editing tags on a question and not being able to get this popup :(