Here's what you'd do...
Do the ATPL exams
Build hours to 150 (minimum for starting the JAA CPL course)
Do the CPL course (training reduced to "CFI's discretion" if you have an FAA CPL) which can also be combined with an MEP course if you so choose
Do the IR course (training reduced to minimum 15hrs with FAA IR)
Apply for JAA CPL/IR
Get an airline job, then once you reach 1500hrs (with a few other requirements) you can take the ATPL checkride