Read my posts #8 and 9 on previous page and then call local authorities in Lisbon to see if they will let you validate your FAA ATP. You still need to get local medical and pass an JAR Air Law exam( I think its open book) before you can fly there. Your operator must train you per their company training manual and then you apply for validation which is based on your FAA ATP ( you must have a type rating on your ATP and a valid 1st class FAA medical the whole validation period). Once approved ( might take up to 4 to 6 weeks) you must take the 14 JAA ATPL written exams. Once they are all done you can get that JAA ATPL at your next sim check.
Make sure you talk to local authorities about the necessary steps and also make sure that your potential employer is OK with all this.
Major pain but cheaper than going to flight school