Playing vs the CPU, I don't think there's any way to get an authentic experience pitching to contact with the hope of being a groundball pitcher.
The movement of pitches doesn't have the effect it does vs human players, you'll have hitters wrapping around a slider, swinging under a sinker(without a tendency to pop up your 4 seamer) etc..
And one thing is for sure, if you pound low zone/below zone, the CPU zeros in and will start lifting low pitches with ease. As ridiculous as it sounds, you have to throw some sinkers/changeups high to avoid some kind of anti location spamming mechanism. Elevating your 4 Seam does help a bit, but nothing close to simulating a GB pitcher.
If you want to do it anyways(I tried a Rockies franchise modeled on GB pitchers and great infield defense), I suggest:
P1: Sinker or 2 Seam
P2: Changeup, pair opposite movements, Sinker with Circle Change, 2 Seam with Straight Change or Splitter.
* I know a lot of people pair up breaks, but the same break is less deceptive than changing both the speed and break. The hitter has already committed to the swing by the time the pitch is breaking anyway, anything to get farther from the barrel is a good thing.
P3: 4 Seam, Use it up in the zone, change levels, throw for low strikes if the hitter is laying off low balls. (Won't work vs CPU, but you can tell yourself it does.. It's a great putaway pitch when the CPU is fouling 12 0-2 pitches in a row)
P4: Slider/Cutter/Curve, Pick one, a curve is generally a pitch guys get under unless you snap it off and make them miss, or bury it in the dirt. Sinker ball pitchers usually have good splits vs opposite handed batters, so this pitch is just to be filthy vs same handed with something that breaks away from the bat. I would go for a Cutter, easier to throw strikes and get weak contact, keep the pitch count down.
No need for a 5th pitch, but if you want one, pick something for when you need a strike out, Slider's a great option.
Focus on H/9, and good 'ol overpowered pitcher fielding attributes.
Good luck