Contributing vscode configurations which are activated conditionally

I am contributing some configurations to VSCode through my extension. I want some of the configurations of my extension to be enabled/disabled conditionally.

For example, I have a boolean config called "Enable Plugin Developer Mode". I want some other configs to be provided when I am in plugin developer mode and I just want to see them only if I have already enabled the plugin developer mode.

I have tried to achieve this through json schema if-then-else, but it seems not working.

"configuration":{  
   "type":"object",
   "title":"MyExtension",
   "properties":{  
      "myext.mode.developer.enable":{  
         "type":"boolean",
         "default":false,
         "description":"If set to true, Developer mode will be enabled"
      }
   },
   "if":{  
      "properties":{  
         "myext.mode.developer.enable":{  
            "boolean":true
         }
      }
   },
   "then":{  
      "properties":{  
         "myext.runtime.path":{  
            "type":"string",
            "default":"",
            "description":"Path to runtime"
         }
      }
   }
}