Actually, since this is a many to many relationship I am going to create an intermediate object.
The issue is that I am going to manually populate the data from within the custom function I will be writing. I have not been able to find any wpcf functions I can call to create the intermediate objects, so I will have to write out the records to wp_posts and wp_postmeta directly. Looking in the database for a similar intermediate object I already have in place, I see 2 wp_postmeta records with _wpcf_belongs_xxx meta keys pointing to the linked posts post IDs. There is a third record with a meta key of _edit_lock; it has some sort of numeric value – if I am setting that manually what should it contain?