eating and eating

Yesterday Isaac discovered he liked chocolate muffins - not a food we would have tried but he found some on the floor! Paul then gave him a whole one and he ate a lot of it. I found some cheese straws which looked fairly high calorie and he demolished a few of them too.
Today he just finished a small bowl of custard mixed with cream and then some mashed avocado and banana.
I spent an interesting time reading up calorie values of everything he might eat. His tube formula, Nutrini energy has 150 calories per ml, ordinary baby milk has just about 50. I decided to try making up baby rice with warm nutrini but it turned out rather grey looking and not very tempting to Isaac.
A dish of baby rice is 20 calories for the rice, 25 for the baby milk, 20 for golden syrup and 25 for cream. The dietician reccomended 1300 calories a day at our last visit and it is going to be very hard to get this number of calories into him with food alone.
We really want him to start drinking as then we can get in plenty of calories with baby milk and cream.
Last night for the first time we didn't feed him at all through his tube overnight, but have had to give him 200mls water through his tube after breakfast this morning as he looked so floppy. He picks up almost magically with a bit of fluid.
I keep offering him water through many different cups but he will only take a sip or two - I'm trying to avoid bribery but did end up only singing his favourite animal song to him if he took a sip. I've tried baby milk and chocolat emilkshake and ribena but they make much more mess and smell when Isaac throws them everywhere.
We will keep giving him fairly liquid food I think until he feels confident about swallowing thin liquids.