Custompress (or functions.php) question regarding adding a dynamic drop down custom field?

Hi all,

I have a question about adding a custom field to a post type. I want to add a drop down that pulls the article list of a certain post type called experts. Basically I add an article to the experts post typeand I'd like to pull that expert(/article) up in another post type called sectors. how would I pull the article listing up dynamically as a drop down.

I see custom press only allow static fields. How would I go about adding this to my functions.php?