I can understand your position on not donating for "such a simple feature". That's not a problem for me and I welcome your taking such a stance.
In any case, the free Testimonials Widget 2.3.0 release update provides several new filters, one of which,
testimonials_widget_content, is the same that I'm using for incorporating the 'read more' links.
You and other developers are very welcome to code your own version of Testimonials Widget Premium plugin's caching and 'read more' link capabilities without donating.
Personally, it was a hard choice making the 'Read more' link feature a premium option. I knew that there were going to be people not happy with me for doing so. However, I feel that asking for donations are an acceptable request to help pay for the normally free and ongoing support and development like Testimonials Widget's 17 high-level changes to go from version 2.2.9 to 2.3.0.
Furthermore, if someone can't afford to donate, they can always email me directly, not via the forums, and ask politely for a copy of the premium plugin. The support email address is found under the "Support" heading at http://wordpress.org/extend/plugins/testimonials-widget/.
Lastly, the Testimonials Widget Premium plugin is an add-on, rather than a replacement for the free Testimonials Widget plugin. The Testimonials Widget plugin is required to be installed and activated in order for the Testimonials Widget Premium to work.