There's only six countries that have adopted JAR-FCL 4. Ireland, Netherlands, Germany, France, Denmark and Sweden.
There is some guidance on what the requirements are for converting a non-JAA license in part 1 of FCL 4. I think they are talking about licences issued by non-JAA member states, so your licence might be easier to convert.
My advice would be to contact one or all of the six states mentioned above and see what they have to say. In your case I would start with the Irish.
Good luck.