Some of the climbing and arctic region peeps have 'trained' their bodies to accept veg oil - just drink it straight down. About the only way to get the calories necessary for staying alive and being able to carry on. I note that Sir Fiennes needed heart bypasses and used this sort of approach sometimes.
I used to cycle a lot - 50 round trip every day to an from work plus 100milers on the weekend. Eating enough calories was very difficult, I ate a lot of butter, cheese and milk-based recovery drinks. This worked to deliver the calories but long-term wasn't a good thing for my health. Best kept for expeditions only, but still I think it wise to train your digestion to cope.