That example actually adds fields that filter the data retrived by the RDL. You only need to include the CallContext table.
Basically 2 setps:
Customize the form and and a text box bound to CallContextBPMData.Character01
Then in the RDL, add to the dataset’s query expression: + " JOIN CallContextBPMData_" + Parameters!TableGuid.Value + " T2"
And add the Character01 query field to the dataset.