I just wanted to add my two cents, since I took this strategy with my application and had success. Provided you can make a very compelling case, it is a perfectly acceptable to say you want to stay within the same company / function / industry. With that said, everything needs to tie in. In my case, I had very clearly stated goals about staying in the industry, but needing additional skills to round out my abilities so I could create change on a larger scale. To re-inforce this message, all of my recommenders (all from my previous company) indicated that they were well aware of my plans and whole-heartedly supported my decision and need to acquire additional skills through an MBA.
From your description of your desired future role, it sounds like an MBA is a requirement (or helps greatly) for a jump in responsibility. A possible approach is to focus on the hard finance skills that will help you move up, plus some well-defined management / soft-skills that you feel you will need to lead in a more advanced technical role. It might be helpful to focus on the short-term jump in responsibility, but also your long term goals - what will an MBA provide in terms of long-term development?