Hey Tilly - I don't there is any clean way to do this right now. There are options that you could explore such as spreading the Parts 2 - 5 articles out into a different Knowledge Base and excluding that Knowledge Base from being searched on your portal. You would effectively have a dedicated Knowledge Base for 'Parts' type articles then. If you were to explore this you would really want to make sure that your Part 1 contains the correct link to the next part.
Another (simpler) option could be to improve the searchability of the 'Part 1' article. You could do this by adding values into the 'meta' field on the item to add more keywords that users typically use to search this article. That will help make sure it is the first one that comes up.
As an aside - if you're not doing this already you should probably add Parts 2 - 5 as Related Articles. I.e. Part 2 is related to Part 1, Part 3 to Part 2, and so on and so forth.
