import from custom cms

I want to import posts from a custom cms into a wordpress mu install. The mu install has over 280 subsites. The posts from the custom cms are all in the same table in a mysql db.

I found a great article by Yoast that has worked for me to a degree but I’m stumped on one part. Here’s the link to that article: MySQL to WP import

Are there any suggestions as to how would i get this to import articles to a different subsite post table depending on data from a specified row in the exisiting cms db? Example: there is a column called facilities with a number 3 in it. How would i get that article to just import to the wp_3_post table and not the main wp_posts table?

Thanks