Ward, the quickest way to do this is the following:
- get a US validation PPL, the well-known piggy-back license or 61.75
- pass a FAA IR written test
- training as required to pass the IR practical test (12-15 hrs.)
- pass a FAA CPL written test
- training as required to pass the CPL practical test (12-15 hrs.)
Airmen Certification - Verify the Authenticity of a Foreign License, Rating, or Medical Certification Before somebody mentions it, yes you can get a validation for your JAA IR also but it is only valid for recreational PPL purposes and doesn't carry over to a US CPL.
Therefore the need to get a stand-alone US IR.
I assume you'll be flying something fast SE like a Saratoga or maybe a TBM?
Get some time in that also while you're in the US.