I imagine there shouldn't be an issue with being able to keep insulin at the college. The practicality of that may depend on how you take it, ie if you use a pen, you may not have a spare that you want to leave at college, however if you use needles and vials, then maybe it'd be possible to leave a vial with some insulin in and a couple of unused needles in a first aid box in the staff room.
It may be worth having a chat with your union rep first, and getting them on saide before going to staff, as if the staff get the funnies in the first instance, going to the union afterwards may get you on the wrong side of the staff, however if you go to the union first, and then mention that to your tutor, he/she may well go along with the proposition just so as to avoid allegations of discrimination.
I have no great love for student or trade unions, as I see then as a bunch of Mafioso style protection racketeers, and driving force of the fascist state we now live in. however one man's terrorist is another man's freedom fighter, so if the NUS can help you, then maybe that'd be worth a go.
Failing that, just make your excuses and go home if you've forgotten it in future. If your BS goes too high, you'll not be focusing on your work anyway, so if you're not going to get the work done, might as well not get in done with an average BS rather than a high one.