Kevin,
I used colonics prior to my last colonoscopy and then had it done without sedation. I've posted in several forums about it. The Optimal Health Network also covers some of the issues that you might want to consider with the other suggestions.
I scheduled a colonic in the afternoon, 24 hours before, and another the morning of my colonoscopy which was scheduled at 1:30pm. I had begun the clear liquid diet the night before my first colonic. It is critical to assure that nothing solid is coming down the digestive tract from above the large intestine.
I took a good cleansing enema before bed and then had the colonic as scheduled. The colon hydrotherapist knew of my plan and filled me several times to the cecum. She had prepped other patients this way and had finally gotten positive feedback from doctors. I made sure to keep my electrolytes balanced.
I had the second colonic in the early morning, again with several fills to the cecum (110 oz). There was about 2 hours between the colonic and the colonoscopy to allow my colon to dry.
The colonoscopy wasn't overly uncomfortable without sedation. The only discomfort was in the first bend during insertion of the scope. I was alert and talked with the gastroenterologist throughout. The whole process lasted about 20 minutes and I didn't need assistance and walked to my car and drove home.
The nurse who attended me said she and the doctor were skeptical that I would be able to deal with the discomfort. She made a comment about how bad the oral prep usually is and I told her after the fact about the colonics. She said she was likely to consider a similar arrangement for her own procedure that was coming up.
For those who routinely use enemas for health or play, the scope isn't much different than a long colon tube and the enemas or colonics are rather enjoyable. The only embarrassment was the passing of gas afterward. The staff understands. It was more convenient for them also as it relates to sedation and being able to communicate with the patient during the procedure.