I actually used your implementation of the fake-jstestdriver.js as template for this code. 
This is how the TestCases are build there (line 61).
I wasn't sure how you usually implement inheritence models so I thought I would use one that you are already using. Basically all I am doing there is creating a constructor method (as far as I understand it ;-) ) which will then be used to construct the different data handlers.
I am open for a different implementation of the same logic... I just thought since this is google code it probably is pretty smart :-)