I believe the FAA will/would issue you with a PPL based on your UK licence - not sure what the situation is now after 9/11 - sure a search will get you the lastest info.
For a CPL it used to be a case of just take the exams and a checkride for licence issue, again not 100% sure of the situation now - no 14 exams and all the associated hoops to jump through.
Guess the school who will hire to me may be wrong but I don't think so, if you read the following CAA link - CAN'T work but the original question does refer to commerical gain except a free ride.
CAA FAQ