A question about submitting parameters using Ajax.Updater

How can I use Ajax.Updater to send parameters from HTML - param1 and
param2 the values of which are not in a form as such using
Ajax.Updater in a manner such that on the server side, I use the
model's update_attributes method.

new Ajax.Updater(
      {asynchronous:true, evalScripts:true,
parameters:'authenticity_token=' +
encodeURIComponent('Hl7TS7DG2dM0zmGAO09HMU8rKTNJwto37APahAPK9vA=') }

How can I modify the Updater above to generate the data below so that
I can use model.udate_attributes(params[:some_model])

{ "authenticity_token"=>"Hl7TS7DG2dM0zmGAO09HMU8rKTNJwto37APahAPK9vA=",