brindle, there are always the old hospital standbys - broth (chicken or beef or onion soup without the onions - run it through a sieve) and plain jello. Ensure is available - don't know if it tastes good. My friends put five fruits with 100% cranberry/grape juice in their blender until it is completely a liquid and drink it for breakfast every day. (Apple, banana, blueberries, kiwi and sometimes strawberries or an orange - with a few leaves of spinach for good health!) I would strain it before serving for a total liquid meal, though. Almost everything can go through a blender and become liquid with broth added, if being clear is necessary.
You always have your Mist, Seven-Up and Ginger Ale if his drinks must be clear.
Check with his doctor and see if he can have milk products - a banana shake or a strawberry shake - thin ones as opposed to thick ones.
Vanilla ice cream and orange juice in the blender tastes like a creamsicle. Sharon (my wife) loves it. You didn't say why he needs a liquid diet... some things that are liquid, like shakes and such, do not meet the requirements depending upon the reason for the restriction in the first place. He may require clear liquids. Also I wouldn't be to concerned about nutrition if it is just for a day or two. Nutrition doesn't work that way.