I've spent some time thinking about this in the past because my former long-term partner wanted to get out of being a management accountant into working in startups like me.
By the time a company is looking to employ a CFO or even a full-time accounts person, they're probably no longer "a startup".
From my experience financial service startups tend to either have founders with domain experience or actually rely on a third party platform for the financial service aspect. To give examples of that, BankSimple's two founders "previously consulted in the banking sector" (whatever that means) and Mint was really about lead-gen - the actual financial services bit was handled by a 3rd party platform.
I even know that one of the popular '2.0-style' online accounting sites doesn't even have anyone professionally qualified to do accounting on their staff. They just read books or ask accountants as needed for product advice.
If I was a VC I wouldn't invest any money in a financial services startup that was relying on an employee to provide the domain experience - it's got to be at the founders level (or like Mint, not actually about financial services at all).
The bottom line is that there are plenty of smart, professional people out there whose background, experience and qualification simply don't offer much to a startup.
The only real option I can see for your friend is to actually start a startup himself/herself and be the CEO. The financial services experience will help them with running the business (accounts, planning, etc) but their management consulting experience may be a hindrance when it comes to leading and managing a bunch of hackers.
I personally would never hire an MBA to work in a startup, in any position. Perhaps your friend doesn't have an MBA but hopefully you can see where I am coming from.