It would be possible, but time-consuming. Smoothies/shakes and nuts, as someone said above, would replace a lot of the nutrients. You can throw a ton of calories into a shake and down it pretty fast. Even if it tastes bad (not that it has to), it's pretty quick, and therefore not too painless.
But yeah, this is totally plausible. When you think that the average adult male eats something like 2,000 to 2,500 calories a day, more if they're over-eaters, this makes plenty of sense. Swimmers are the same way. High-intensity cardio will suck the life out of you if you don't eat like that.