Although this is not strictly an answer to your original question, I might remark that drop height is not the only variable that determines Poseidon's response aka fluid flow. Also shape plays a very important role, as you might have experienced while carrying a plasterboard before you during a ride on your bike back home from the hardware store.
We know that a streamlined body ("drop shape") exposes quite low a resistance to the surrounding fluid (it has a low drag coefficient). This will cause less of the water in your john to be set in motion, which will also lower ejection into the direction of your bottom as a consequence.
One thing you might also consider is the fact that, although you cannot control the velocity of your "logs" in free fall, longer turds still adhere to the outlet and hence, their velocity is largely determined by friction between the former and the latter.
The relationships from the last two paragraphs should open up a multitude of possibilities for influencing the impact speed by controlling your musculus sphincter, musculus rectus abdominis and musculus pyramidalis. Also, nutrition and drinking habits might have a significant influence on excretion consistency. Some things you could try: onions, coffee, cabbage, eggs, etc., you get the idea.
Disclaimer: this is not a medical advice. Be sure to see a doctor before experimenting with your body.