I'm not aware of any agency that will offer a certification based on experience - the standards for certification are there for a number of reasons - yes, of course, there is the financial incentive for the dive centre and instructor - but also the legal implications of certifying a diver. The standards are set and they must be adhered to prior to certification (and let's not get into the typical agency-bashing session here!!) It may well be that you are an expert FFM diver and - as you state - not trying to skirt the rules, but as instructors, we really can't make exceptions; if you should have an accident and the authorities determine that the instructor did not follow the standards, this is very bad, regardless of what training you may have had before. It's something I've encountered quite a lot over the years and there's this situation where, as an instructor, you have to teach somebody who's more experienced in something than you are!
Having said that - you are only required to meet the standards for certification - which usually involves demonstrating some knowledge of theory and some practical skills, then perhaps you can agree with an instructor to do a short form of the course and therefore save you time and money. A few probing questions from the instructor should suffice and then a pool session or whatever is required (I'm not a FFM instructor) for certification. All boxes ticked, certification issued. I also have to add that I am not advocating short-form training in all but the most exceptional circumstances.
Hope that helps a bit - let us know how you get on.
Cheers
C.