External Attributes: Dynamic Drop down list in Windchill

I am unable to use the Cascading Attributes functionality in 11.1 M020 because both of my attributes (ex: attribute1 & attribute2) are to be read from a list in a property file on the file system.

I have an attribute1 that generates a pull down list of selections using a ComboxBox. Based on the selection for attribute1, I would like to dynamically update the pulldown list of values available for attribute2.

I have looked at:
CS138327 (returns an enumeration list but I don't see a way to relate attribute2 to attribute1's value)
CS226468 (only returns a string, so unable to create a pull down list)

I have tried using a ComboBox and the addJsAction method but it looks like this will not work in 11.1. Any ideas on how one would go about implementing this in 11.1?

Thanks for your time.
Troy