What is the protocol with regard to piggybacking questions

Question

Here is the scenario:
I have a question and that I want to post on SO.
So I type in the question and very carefully parse the similar questions list.
The exact (or near-exact) question comes up in the list, so I go to that question and parse the answers and comments.

The original poster is clearly not English first language, but I understand what he wants because it seems it is the same problem I am facing (98% sure). None of the responses are helpful to me, however the question could be phrased better.

Can I post an "Answer" as a re-phrase of the question?
Is it okay for me to "piggyback" on this question?
Is it okay for me to add additional "what if"'s and *"I also need"*s?
What is the etiquette on SO regarding this?

Edit
Thanks for the helpful responses. I will post a new question and reference the original or (inspiring) question.

Answer 1

Don't piggyback on his question.

If the original question just had really poor grammar/formatting/etc. but was basically the exact same question, then try editing his question first, if you have enough reputation.

If you can't edit, ask a new question and explain in a footnote why you're doing it (i.e. it's not an exact dupe because of X, or that you felt that the original question was poorly-phrased and that was why it had no answers/bad answers).

Many of us, if we want to duplicate a question that was very poor due to author laziness or language difficulties, will ask the new question and then vote to close the old one as a duplicate of the new one. If you don't have the reputation for that, you can request (preferably in a comment) that if other people wish to vote to close, that they please close the old question because it was poorly-written and didn't receive any good answers.

No guarantee that they'll listen to you, but it is still far better than asking follow-up questions in the answers. Don't do that.

Answer 2

It's not okay to piggyback questions in the form of answers. Create a new question, reference the old one, and make it clear how your new question is not a duplicate of the old one (saying "this is not a duplicate" is not enough).

In terms of follow-up questions, they should be limited to clarifying received answers should you not understand them or if you do not believe they adequately answer your original question. Otherwise, you should be creating new questions for your new issues.

The important thing to keep in mind is that Stack Oveflow is not a forum: a question is not analogous to a forum topic.