Sidebar widget – Show random testimonials

I set up this plugin as a side bar widget.
I entered 20 testimonials.
Now I want to limit the plugin to show only 2 testimonials (this is a simple setting in the widget settings). However, i want the testimonials to display randomly.
Meaning, each time you refresh the page it should display 2 different testimonials.

http://wordpress.org/extend/plugins/testimonials-by-woothemes/