hi i been looking everywhere i cant find anything on this. I found code to make it use a one category.
this goes in the functions.php
function my_random_post_args($args) {
$args['category_name'] = 'cat-slug-here';
return $args;
}
add_filter('random_post_args', 'my_random_post_args');
it works like a charm for one cat. but i want it to work for all my cats
link to plugin
http://wordpress.org/support/plugin/random-post-link
[ Please do not bump, it's not permitted here. ]