Funny you should say. I had a 6 month contract position that kept getting renewed. The last renewal or two had very little work--it was mind numbing, for 8 hours a day, every day for months and months.

When faced with a mundane task that offers no learning opportunities, try and get creative within some time budget. When porting some Java source to C++ that included a test suite, I parsed it into ASTs, transformed the AST and unparsed the C++. Of course it wasn't complete as it was a total hack, but it was complete enough that tidying up the output was interesting because it would let me see if the process worked when I got through with it. The best part was not having to write the test suite from scratch.