Have you tried Angel Tuning ?
My other half emailed them about remapping her R27 and they quoted around £350. That's for them to come to you and treat the car to a bespoke remap, not one of the lesser, generic 'Group N' reflashes that most other 'tuners' offer.
Obviously, this is performed on the road and, I'm guessing the owner will be doing the driving whilst the Angel Tuning tech, will be monitoring the ecu, tweaking the parameters and then flashing the ecu with the changes.
This will give you the best results possibleand, they offer a 14 day money back guaruntee, if you're not satisfied with the result.
Just a thought.