Essentially, put in the effort and do the liquid bowel prep.

It's not just about effort. I must do the liquid prep due to my Crohn's disease. And while I am able to get the liquid down (as you note, it helps to make it as cold as possible; also, suck on an ice cube before drinking to numb the taste buds), I can't keep it down. Within an hour it has me evacuating from both ends.

For my last test, I barely slept at all the night before on account of the vomiting, and even once I got to the hospital I was lying on the wonderfully cold tile of the floor between rolling over to vomit in a trash can.

They know it affects me badly, but still assess that it's necessary due to my risk factors. And because I'm losing much of the drug due to the vomiting, the prep is poor, so I have to start fasting a day early to ensure that I get sufficiently cleaned out. It's torture all around.