How to Limit to Only One Post on Pro Sites

I need to know how to get Pro Sites to limit unpaid users to one post at a time per blog. I was told it was capable of this when I asked in pre-sales by Tyler:

"[Y]ou can limit the amount of posts/pages/custom post types they can publish. This will place a limit on posts they can actually create and publish, so backend :slight_smile: ie. If you place a 5 page limit then they can only publish 5 pages."

Need to know how to get that working, all I'm seeing is the option to allow/deny posts altogether, which would take a lot of hacking to get working where I need it.

Thanks in advance.