If they took part of the stomach, it was probably the lower part which includes the pyloric sphincter. That's the muscular opening (sphincter) that partitions the stomach from the small intestine. Without that partitioning, it's going to be very difficult, unfortunately, to keep bile out of the stomach, but it also depends a bit on exactly where they placed the stoma (opening) of/to the duodenum on the stomach when they made the connection. You may want to ask his doc if something like Reglan (which stimulates the motility of the stomach) would help. It's not a drug that everyone can take, and it's dosage/use has to be monitored.
I hope this answers correctly. They took the head of the pancreas, part of the stomach, part of sm. intestine, part of the deodonum (sp?), and gallbladder.
What form of Whipple did he have done. There are various types of Whipple procedure.