How about if you just kept it on, on low, until you'd finished the entire thing? Maybe 2 or 3 days? Perhaps adding a few more mushrooms etc, as you go along?
It is actually my brother's. He lives alone and works very long hours. We thought this was a good way of getting decent food into him. He's a bit of a slob - well, very busy and knackered when he gets home - so not so hot on the cleaning up front.
Trying to think of a way to keep him fed without involving much washing up or effort. If he has to transfer leftovers into a pan to heat up then that's 2 things to wash up. If he were to only do enough for one meal, then he'll just go back to not eating.... but with an expensive piece of junk cluttering up his kitchen collecting dust. Bother.