I think a sequel- in keeping with the whole theme of, well, Bullworth- could just add to the canon they've already provided. I mean, there is still HEAPS open for more storylines and stuff... I'm sad there's no sequel going to be made, because there's definitely a LOT of possibilities for one.
How 'bout Jimmy being a prefect, and having to deal with new teachers, corrupt other prefects, and maybe some type of outside plot to bring him and Bullworth down? (I'm trying not to give away anything that happened in the original because I don't want to spoiler anyone!) The town of Bullworth might have changed slightly (in the same way that GTA: LCS and GTA 3 are set in the same area but have their differences) and extra surprises could be added in... but yeah- it could totally work...