Hey at the moment this is unfortunatly only possible by editing the plugin. That means you need to reapply the change when updating the core or skip uploading this plugin on the next update ( if there is ever a change it would be announced in the plugin thread )
We plan to have plugin child themes available in 0.9 or 1.0, then this would be no issue anymore.
plugins/screenshots/stats_compile_stats.php
Code:
$TMPL['screenshot'] = "<div class=\"right screenshot\"><img src=\"screens/{$screenshot_url}\" alt=\"{$TMPL['title']}\"/></div>";
would become
Code:
$TMPL['screenshot'] = "<div class=\"right screenshot\"><a href=\"{$TMPL['url']}\" onclick=\"out(this,'{$TMPL['username']}');\"><img src=\"screens/{$screenshot_url}\" alt=\"{$TMPL['title']}\"/></a></div>";