Not stackable with the hard achievement, but similar procedure.
The Professor of Catan achievement in Catan worth 30 pointsWin a Single-Player game against three AI opponents set to Hard.Use Fast Play and Fast Start. When you are at the screen in which you choose which CPU players you want to compete against, press Y for options. At the bottom should be the ones you're looking for.
You will start with 3 VP points and only need to get to 7 now.
Adding friendly resources may also help, but it can hinder, too. If you go five turns without income (cumulative, not in a row) then you will get to pick a free resource of any kind. This is great since the CPU barely trades anymore. However, keep in mind that the CPU gets the same perk.
Personally, I went for longest road (+2), built another settlement (+1), built another city (+1).
Going for developer cards might make this easier for some people since they generally help you get resources, you may get a VP card, and getting three soldiers will get you 2 extra VP points.
It only took me two tries to win this way.