They are giving you b12 because it is well known that absorption after a j pouch is low.
But anyhow here is a possible, that they may not know.
Old Mike
You might try vitamin B1 saturation, 600mg if you are about 60kg in weight,the idea is to saturate the blood,so the
b1 can transport into the cells.
http://www.ncbi.nlm.nih.gov/pubmed/23379830