My understanding is that the sticking point for a Brit applying for jobs elsewhere within the JAA area is unlikely to be not getting his JAR licence accepted, but actually the requirement to speak the local language.
This is another area where the JAA sucks for aspiring UK/Irish pilots. Pilots from all countries speak English with a greater or lesser degree of fluency, enabling them to compete for jobs in the British Isles no matter where they originate from the the EU, whereas for us Anglophones to work elsewhere within JAR-land, we'd have to learn Dutch to work in Holland, German to work in Germany, French to work in France, etc. Hardly practical.