Parameters: Select w/ customValue

Is it possible to use customValue with the select type parameter? I managed to get the custom entry field to display when changing {{custom}} to {{customValue}}, but can’t seem to keep it available.

"IDType" : {
    "type"    : "select",
    "label"   : "Type of ID Required",
    "initial" : "Tax ID",
    "options" : [
      { "value" : "Tax ID", "label" : "Tax ID" },
      { "value" : "National ID", "label" : "National ID" },
      { "value" : "Tax ID or National ID", "label" : "Tax ID or National ID" },
      { "value" : "ID Number", "label" : "ID Number" },
      { "value" : "{{custom}}", "label" : "Custom" }      
    ],
    "customValue": "Tax ID"    
  }