Multiple categories for categorized random question selection

I'm using the "categorized random question" selection method in a quiz, and it works really well. But I'd like to be able to do more complex selection than just matching a single category. The most important thing for my purposes would be to have the quiz select (say) 10 questions that match one of three different categories.

At the moment it doesn't look like the module is set up to handle this. Am I missing something? If the functionality isn't there, is it planned for the near future? Or at the very least, could someone point me toward the section of the module code that handles the random selection so that I could work on a patch?

Cheers,

Ian