We could theoretically buy it on the Premium Unlimited Sites thing, however this:
e) You will be invoiced on a monthly basis for the number of active licenses you have created.
From their "web hosts FAQ." Since it's free hosting, I'd venture to bet it won't be enough income from the respective free sites to utilize the software. It'd work on Premium where you could bill users for it, but it might be more hassle than its worth.
There's nothing stopping you from purchasing a single site license and using it yourself however.