marketpress - custom call to the_excerpt function

Hi

I've looked through the template-functions.php file and don't quite see what I need. If Ihave a custom query to the post_type 'products' and I want to call that products exceprt without using the_excerpt (they are all different lengths) - what would my function be?

Essentially I want the mp_product_excerpt function that will replace the WP function the_excerpt()