I recently looked into this vey question for a coworker who is in the same situation. I called AWS Certification department and they said that 40 hrs in anything welding related would work. I suggested MT,PT classes and they agreed that 40 hours in NDE would satisfy the requirements.
Working under the CWI would not meet the requirements.(I asked that too)
You need to attend a 40 hr class and provide AWS with a course description and a certificate of completion.