What is the best way to get a concentrated dose of gluten?

I chose to remove gluten from my diet about 6 months ago. This helped me reduce my IBS symptoms considerably, and with the help of a dietician and further dietary restrictions emergency dashes to the bathroom are now very rare. Unfortunately I have other stomach issues that have not resolved and am on the wait list to have a gastroscopy and endoscopy. My gastroenterologist has suggested I add gluten back into my diet leading up to the tests so they can see how it effects me. I am for this idea, but, I do not want to go back to eating the bread and flour that I have so carefully been avoiding. It isn't the side-effects that worry me, I'm prepared for those, it's just that I have worked so hard to develop my new eating habits, and I do not want to break them. I am also currently on a low GI diet which is keeping my diabetes in check very nicely and wheat products do not fit into it. SO I am looking for a way to get in the gluten equivalent of 4 slices of bread per day without eating bread. Is there a pure gluten source? or at least one that is very high in gluten?