Instead of using fake members, why not use a paid posting service (made up of real people) or do post exchanges?
They're not loyal members, but they're real people. If you're exchanging posts, you're helping out a fellow forum owner. That means something, especially now that forums aren't as popular as they were 15 years ago.
Using fake members, though, feels too much like a lie. Get caught lying to your members, and that's it for your reputation!