I am in the same boat, I have two completely unrelated thoughts on what I want my post-MBA career to be - Real Estate Development or Mktg/Product Management (in a very specific industry). I have been in marketing thus far and have no formal RE background, except from the exposure I received through my father's development company. I am going the safe route and talking about marketing, my "Why MBA" comes in at me wanting to change industries, have a more concrete and formal training in the marketing discipline, and develop more well rounded skills in quantitative and strategic areas to make sound decisions for mktg programs. I know quite a bit about the industries I'm interested in as I had accounts with these major companies in my old position, I also work in the emerging/online space which is a big plus being that it's the new "hot" thing in marketing. I feel like these factors will add more strength to my app than talking about my passion for RE Dev.
Although there is a greater stretch I'd like to go for in my MBA (RE and finance), I honestly feel like not having the prior experience to provide supporting evidence in my essays will hurt, no matter how much knowledge I have of the industry and can convey.
I don't think accounting to I-banking is a big stretch, the only obstacle this goal could face, if at all, is wariness about I-banking recruiting in general, not that you came from a CPA background.