Adding extra calories is pretty straightforward. In times of dire need I am prepared to adopt the 2 dessert strategy: 1 with lunch and 1 with dinner. It's a sacrifice I'm prepared to make to fuel my running.
For a start, use full-fat milk to make the porridge, increase the portion in general and add some nuts, seeds and dried fruit or have a piece of toast and honey with the porridge.
Have snacks between meals. Have nuts/seeds/biscuits - anything with more calories than a piece of fruit. Or if you're worried about not hitting your 5 a day, have something in addition to the fruit.
Eat more than just a sandwich and an apple at lunch. Add some crisps or chocolate. If your exercise is really burning 1000kcal/day, you have to start eating energy dense meals.
Make sure you have a decent sized dinner.