In the years since my Ileostomy (51) I have had a number of studies - barium from oral ingestion, barium via "enema" through the stoma, scpoings through the stoma and have never had a problem passing the barium. Today's mix is much more fluid than what was available 30, 40 and 50 years ago.
I wouldn't worry about it. Just make sure you have an empty bag to start with and access to a toilet soon after the study. It may go through quickly.
Hope it works for you.