I don't know if it would work for a full liquid diet but it worked for me to get enough protien in after surgery. I drink Isopure zero carb bottled drinks. I get them at GNC. They are 40grams of Protein each, a clear liquid in fruit flavors. I mixed each one half with Water to get 40 oz of water and 40 oz of protien per day. I was able to get the other 20 grams in food. It also isn't so filling. I was only able to eat one ounce of food at a time for the first month after surgery. I am two years out and only eat 3.5 oz food per meal now. I looked at this post because my surgery was 4/19/10 :-)
I wanted to loose 80 lbs. I lost 120 and have held it pretty well so far. Lots of walking, wii fit plus. I eat whatever I want (except rice, noodles, not much bread - those flat buns are fine) but in very small quantities. I eat 5 mini-meals a day. I only drink one of these (diluted version) after exercising now. It seems to help build muscle.
The grape and the apple melon taste the best. the others are not very good IMO.THey are made with 100% whey protien isolate.