How do I create a vertical RadioButtonBar in FormObject?

RadioButtonBar has an option Appearance->"Vertical". But I am using RadioButtonBar in a FormObject(basically to create multiple-choice questions), and in the documentation this is specified as "Control"->RadioButtonBar. But that gives the default horizontal bar. How do I specify a vertical set of radio buttons? I can’t supply the Appearance option to RadioButtonBar without some button specification arguments first, but in the context of FormObject those are picked up from the other parts of the FormObject spec. Here is an example of a FormObject that give horizontal buttons:

form3 = FormObject[<|
   "Response" -> <|
     "Interpreter" -> {"None at all." -> 1, 
       "Some stuff in high school." -> 2, 
       "I have taken one or two intro-level college classes." -> 3, 
       "I have written code for research in an Independent Study or similar." -> 4, "I have mad skillz and write my own apps." -> 5}, 
     "Control" -> RadioButtonBar|>|>]