I agree with PP -- cereals, meat casseroles, and other carbs will help fill him up a bit more. When he wakes twice at night, is it to eat? If so, you can try increasing calories during the day to reduce or gradually eliminate night feedings.
For comparison purposes - and I know all babies have different appetites, but my DD is 6 months and 14 pounds and this is her feeding schedule (not always at these times exactly):
7am BF
8am 2 tbsp cereal, 2 tbsp fruit
11am BF
12pm 2 tbsp veggie, 2 tbsp meat, 1 tbsp fruit
3pm BF
5pm 2 tbsp cereal, 1-2 tbsp meat, 1-2 tbsp veggie
7pm BF
Let us know how you make out.
Jana