Maybe I'm not understanding the application, but I don't think that simple text matching for these assignments wouldn be all that difficult. I'd be interested in pursuing it, Martin. You can contact me directly.
I know a computer science teacher who has a high school student who wrote something much more involved for evaluating and testing submitted Java code. They even integrated it with a plagarism checker. It's called JAMtester, and can be found at http://www.jamtester.com/.