Diet Coke is one of the worst chemical concoctions you can consume. The sweetener Aspertame can cause various neural unbalances including mimicking the symptoms of Multiple Sclerosis. It also keeps your craving for sweets high and can actually contribute to weight gain. Go to Mercola.com and do a search on aspertame. There are plenty of warnings here on Curezone and other sites too. Stay away from this stuff whether you are cleansing or not.
About the only ingredient you can really take separately in the Master-Cleanse drink is the cayenne. You can take the 1/10 teaspoon in a single "Shot" of drink, use cayeene tincture in a small amount of drink, or many people take capsules (although some have had troubles with this approach).