timt said:

I would like to also set up the role_scoper permissions on this new post automatically, so that only specific Groups of users are Readers of the post.

I tried writing new entries to the wp_user2role2object_rs and wp_role_scope_rs tables to achieve this, but this doesn't seem to be enough. 

Did you create the desired restrictions / roles manually and then confirm that your code is inserting equivalent entries? You shouldn't need to modify anything else (aside from flushing the cache as you mentioned. Of course you can always manually flush or disable the cache if you suspect that your own cache-flushing call is faulty.