Maybe don't hire them as staff? Have it as like a community role, you could get people to apply for the roles or you could approach people from each section of the forum and ask them if they want to undertake the role. You could reward them with VIP or something, but they wouldn't actually be staff, they just have a role to post thought provoking threads to get people talking and in return they get VIP. You could have different debates leader each month? I dunno how you could work it but i think this is a really decent idea to get people posting more though provoking threads, rather than just millions of threads asking for help.