strategies to secure more independence in a postdoctoral position?
First of all, let me say that your choice of words really rings an alarm bell with me. The general impression is that you are very ready to be inhonest, and (in agreement with that) your default position seems to mistrust your future employer and you seem to expect suspicion as opposed to taking in the situation openly.

Now if someone does not trust me, a natural question for me is: why should I trust them? I would not want to work with someone with this attitude towards work. And moreover, I wouldn't want to have someone messing up the working atmosphere in my group.  

(But don't worry: I'm not in the position to hire anyone.)


  Do I need to sell my PhD work as my own idea in a postdoc application, or is it reasonable to be honest?


I'd say it is even necessary to be honest, and it is most probably futile to try to get away with anything else. Academia is a small world, and phone, skype and email reach very far nowadays. Particularly if you say that your field is so small that you do not care to name it here.


  Will it arouse suspicion in an application to propose research in an area which is not closely related to my PhD research?


No. But you should have a positive reason to apply there.


  If I want to be able to develop my own ideas as a postdoctoral researcher, should I seek to clarify that goal, seek positions which advertise that option explicitly


I'd say that you are expected to develop your own ideas in a postdoc position.

So: Yes, why not. I had interviews where we discussed openly how much own ideas would be possible, welcome, and what the bottomline of things-that-need-to-be-done-no-matter-what would be. 


  From my observation and reading, there's an art to developing a research objective/question. Ideally, I would like to have some kind of guidance in doing so. In my experience that is unrealistic. How can I seek meaningful mentorship, but somehow frame it in a manner that allows me to move forward and to maintain financial and intellectual freedom from the mentor? 


I can ensure you that there are good mentors and leaders, including also mentors and leaders who are even good at teaching leadership in research. But such learning can only work if you trust your mentor. That in turn makes financial and intellectual dependence a non-issue. It may not be easy to find a good mentor. But on the other hand, you could also learn from someone who is not your direct supervisor. That way, you'd have the financial and intellectual freedom.



But: if you feel you need mentoring how to develop research questions, how can you feel ready to apply for a postdoc position?


  I did not develop my own research ideas or objectives as a PhD student. This was just the state of affairs and there wasn't much I could do about it.


How come? How could your supervisor prevent you from thinking your own thoughts and from having your own opinion and judging of what needs to be done and how? As a research professional, crititcal and independent thinking is one of your core tasks.

Remember: you were a professional already when you started the PhD. If that wasn't necessary, it would be appropriate for an apprentice to apply for a PhD position.
And if you had gone to work in industry instead of in academia, you'd aslo have been profesionally responsible for everything you do.