Dynamic interaction between parameters in Vega Lite?

Question

Link to minimal working example. Here is the part of the code I am dealing with:

"params": [
    {
      "name": "Supervisor",
      "value": "Amy",
      "bind": {"input": "radio", "options": ["Amy", "John"]}
    },
    {
      "name": "Name",
      "value": "",
      "bind": {"input": "select", "options": ["Jane", "Sam", "Bill"]}
    }

I would like the input for Name to be conditional based on the current value of Supervisor: If Supervisor == Amy, display "Jane", "Sam" under "Name". If Supervisor == John, display "Bill" under "Name".

I tried to use the Vega Lite "condition" property, but it works only within mark channels. This was my idea:

"params": [
    {
      "name": "Supervisor",
      "value": "Amy",
      "bind": {"input": "radio", "options": ["Amy", "John"]}
    },
    {
      "name": "Name",
      "value": "",
      "bind": {"input": "select", 
      "options": 
      [
        "condition": 
          [
            {
              "test": "Supervisor === 'Amy'", 
              "value": ["Jane", "Sam"]
            },
            {
              "test": "Supervisor === 'John'", 
              "value": ["Bill"]
            }
          ]
    }
  ]

I then tried exchanging params for signals, but found that "transform": [{"filter": "datum['Supervisor'] == Supervisor"}] would not work when Supervisor is not a parameter.

Will I have to progress to Vega for this functionality?