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Your problem statement is very close to something we are currently doing with the Problem Report workflow as well. I cannot answer the question directly, but part of what we're doing is based on a slightly different approach. Perhaps this might give you a different perspective.
We also want to route a task to a user based on a prior user selection. Our approach is based on something we did successfully for a promotion workflow:
Our approach means that the lookup table is not really configurable by container (though we could mimic that by adding another column), our need does not require it. Maintenance of the lookup table is done by a simple web gui outside of Windchill, for admin staff.