gistfile1.rbx

#!/usr/bin/env ruby

require 'rubygems'
require 'rbosa'

sp = OSA.app 'System Preferences'
se = OSA.app 'System Events'

sp.current_pane = sp.panes.detect { |p| p.properties[:id] == 'com.apple.preference.keyboard' }

sp_process = se.application_processes.detect { |p| p.name == 'System Preferences' }

window = sp_process.windows.detect { |w| w.name == 'Keyboard & Mouse' }

# switch to 'mouse' tab
window.tab_groups[0].radio_buttons[2].actions.detect { |a| a.name == 'AXPress' }.perform

# click on 'right' for primary mouse button
window.tab_groups[0].radio_groups.first.radio_buttons[0].actions.first.perform