Take a shower, or sit in the tub if you're dizzy, then after you dry off, put K-Y jelly on there. Also, after you go to the bathroom, cool off a wad of toilet paper with water, put the jell on that, and dab it there. Clean your hands with alcohol if it gets messy. You are gonna be mighty wore out and sick from all this, but the sedation they give you for the exam will end the whole thing.
You need to get zinc cream. It should be used both before you start emptying your system as well as after every bowel movement.
It helps even after you start tho.
Good luck
There isn't much you can do. I spent about 12 hours on and off the toilet before my colonoscopy.
The interesting part is that the colonoscopy itself is actually easier than getting ready for it.
For future reference, there is a new procedure available where they don't even have to stick a camera in your nether regions anymore...might want to ask your doctor about it.