Using wp_trim_excerpt to get the_excerpt() outside the loop

I’m building a theme that is going to show excerpts on the homepage for potentially dozens of posts. I don’t have manual excerpts on all of my posts, so $post->post_excerpt is empty for many posts. In the event that there isn’t a manual excerpt, I would like to use the built-in get_the_excerpt() function, but it isn’t available outside the loop.

Tracking down the function, it looks like it uses wp_trim_excerpt from wp-includes/formatting.php to create excerpts on the fly. I am calling it in my code like wp_trim_excerpt( $item->post_content ), but it is simply returning the full content. Am I doing something wrong?

I know that I can create my own function to create an excerpt, but I like to use built-in functions where possible, keeping my code compatible with other potential plugins / filters.

http://adambrown.info/p/wp_hooks/hook/wp_trim_excerpt?version=3.0&file=wp-includes/formatting.php

Since WP 3.3.0, wp_trim_words() is helpful if you’re able to get the content that you want to generate an excerpt for. Hope that’s helpful to someone and it saves creating your own word counting function.

http://codex.wordpress.org/Function_Reference/wp_trim_words