Are you sure that you have attribute mapping set up correctly? As long as the mapping is set up and the parameter exists in the Creo start part, it should populate the Windchill IBA upon upload of the CAD Document in the workspace.
Please refer to the the "About Attribute Mapping" Windchill Help Center topic for more information:
Or the "Mapping Creo Parametric Parameters to Windchill Attributes" section in the Using Creo Parametric with Windchill Guide