There is a "demonstrated ability" option under JAA but this is available only for renewals, not for initial medicals.
The reference is
here and the demo ability option is in Appendix 16.
Additional details
here.
The CAA used to do a concession that if you failed the initial limits, but "would have passed" the renewal limits, they would say to you that if you do the IR and pass the checkride, they will then give you the medical. This was in the days when the initial limits were stricter than the renewal limits. I don't know if they still do this, now that they are the same.
Has anybody managed to get any JAA IR with one ear below the limits?
I know somebody tried the demo ability option several times, even after flying IFR on the IMC Rating for a few years, and no amount of references from instructors was good enough; the CAA absolutely refused to allow IR training.
This little thing stops many pilots (private IFR pilots tend to be older people) ever doing the JAA IR. They go the FAA route instead - you can be an FAA ATP and not have to do this stupid autiogram.