Does anyone have any ideas how to increase food intake?!

Argh, we're struggling again at the moment - I know what's new?! J lost a pound while he was in hospital and is back down to 17lb 13oz at 17 months. Back on the 0.4th centile having hovered between the 0.4th and 2nd for a couple of months. I know it's not much difference, but he is feeling very light and boney again
I just don't know how to get more in him. He has his Infatrini (high calorie formula) but he doesn't even drink that much of that, he is prescribed 600ml a day but never manages that. Today he managed:
Breakfast:
A handful of dry cheerios
A whole weetabix with Infatrini
Infatrini in a cup
More Infatrini in cup mid morning
Played with some toast and butter
Lunch:
1/4 small pork pie mostly eaten
red pepper sucked not eaten
1/2 fruit scone with butter - enjoyed but I picked a lot up off the floor at the end
More Infatrini in his cup - this finished one bottle of 200ml over the morning
Tea:
cheese omelette - played with, picked out some cheese to eat
peas - 5 ish
ignored the mash (threw the fork on the floor)
1/2 a yoghurt
Bedtime - Infatrini in bottle - maybe 100ml
I don't know how else to increase his calories - I'm giving him fatty foods as much as poss. His diet seems incredibly unhealthy to me but I'm more bothered about the calories than fruit and veg. He just needs to eat more of it/drink more Infatrini but he just isn't that bothered. What else do I do? I'm doing everything the dietician advised and it works to some extent till he gets ill again, which he does regularly!

Breakfast:
A handful of dry cheerios
A whole weetabix with Infatrini
Infatrini in a cup
More Infatrini in cup mid morning
Played with some toast and butter
Lunch:
1/4 small pork pie mostly eaten
red pepper sucked not eaten
1/2 fruit scone with butter - enjoyed but I picked a lot up off the floor at the end
More Infatrini in his cup - this finished one bottle of 200ml over the morning
Tea:
cheese omelette - played with, picked out some cheese to eat
peas - 5 ish
ignored the mash (threw the fork on the floor)
1/2 a yoghurt
Bedtime - Infatrini in bottle - maybe 100ml
I don't know how else to increase his calories - I'm giving him fatty foods as much as poss. His diet seems incredibly unhealthy to me but I'm more bothered about the calories than fruit and veg. He just needs to eat more of it/drink more Infatrini but he just isn't that bothered. What else do I do? I'm doing everything the dietician advised and it works to some extent till he gets ill again, which he does regularly!