JAR rules I believe allow a one year, one-time, non-extendable waiver to operate JAA registered aircraft with a non-JAR license. I am not sure if Netjets would take advantage of this possibility by requesting a waiver for an ICAO-licensed pilot through the Portuguese INAC. I do know that Netjets does request waivers for European national licenses that are not able to be converted to JAR (these are not limited to a one year max length). My suggestion would be to apply and discuss the issue with the recruitment people.
Another important issue is whether one has the right to live/work in Europe.
Finally, it is not impossible to fly for Netjets and study and pass the JAR exams - but it is not a walk in the park. Requires a very significant amount of time studying manuals and/or going over and over the question banks on line.