Is there any bloat? i.e., is the stomach hard? if his stomach is suffering from bloat, then you need your vet to use the tube idea to suck the gas out first.
If it is just a little bit of gas, you can get 2 ml of infacol every few hour just as a pre-caution.
If the stomach is not hard or expanded, then it's just a GI stasis, you need to force feed your bun for the time being:
Firstly, keep your bun indoor in a warm room, as he can't fight the cold at night and fight whatever health problem he has.
1) Get some non-meat baby food, use a syringe to suck up the baby food, get a cup of hot water, dump the syringe in the hot water for 2 min., now the syringe is warm, so you now syringe feed the baby food to your bun.
Every 1Kg of bunny weight, get 100 ml of food inside him per 24 hr.
OR
2) Get some blackberry or raspberry, smash it via juicer. You need about 6 oz. Get some hay stem, cut the stem in 1 mm length, mixed it w/ the blackberry. Put the mixture in a 35 ml syringe and force feed your bun. Your bun need the fiber to survive.
Here's a useful link on GI stasis:
http://forums.rabbitrehome.org.uk/showthread.php?t=124510