If he is in pain you need to get him to a vet and your vet should have an emergency number to ring.
Sorry dont know about pancreatis but usually the rule is cats need to eat and its better to feed them what they will eat rather than nothing. However somethings may be very bad for this condition but just dont know.
As long as the food you give does not cause pain then it may possibly shorten the cats life but its no good feeding what they wont eat, cos not eating will kill them very quickly.
Have you done a search on this illness because their will be loads of info.