Splashes become a worry once you hit the high end of five feet, which is why this Japanese "Angels Knee Pillow" is a decent alternative, even if it is a little degrading.

The pillows come in two options, a split-mode one and a larger, single unit variety. It's pretty gross when you think about getting your junk THAT close to the toilet, but even grosser if you're so short that your goods actually touch the rim of the bowl. An easier solution would be just to pee sitting down. [House Doctor via Inventor Spot via Crunch Gear]