creating random selection of data in categories

I'm new to xerte and trying to create an extremely interactive course which will also serve as guide for using the software. I've created an exercise of word category but would like to limit the choice of words to move into the categories to say 12 out of a database of 50 words. Is there a way to do that or do I have tweak the programme myself? I do realise that I could create several smaller databases but are fully aware that reloading rather than changing activity tends to attract students more.