Comma Heterodoxy

In my last post I wrote:

A. “This is an ingenious, and, after a bit of thought, plausible, justification.”

An alternative is: 

B. “This is an ingenious, and after a bit of thought plausible, justification.”

    The conventional punctuation would be, I think, 

C. “This is an ingenious, and, after a bit of thought, plausible justification.”

or 

D. “This is an ingenious and, after a bit of thought, plausible justification.”

   Which is best?  I like A and B because they follow the spoken rhythm better, with a preference for B now that I've thought about it longer. I'm not sure about whether there should be a comma after "ingenious". Any thoughts?