There is a short written test. (AMA document 515)
You must be "signed off" by two AMA CD's (one of which must be a "approved turbine CD") (AMA document 516)
You must be signed off by a turbine manufacturer as having been trained on the operation of the engine. (AMA document 517)
You must sign a statement saying that you have flown more than 50 flights with an aircraft capable of flying at 150mph or more). (included in document 515)

All of these documents are then submitted to the AMA and if approved by the turbine committe your waiver will be sent to you.

All of the AMA documents are available here: http://modelaircraft.org/templates/a...1349CAD343278E

The complete requirements are listed in document 513