Currently I'm not considering it and I'm sticking to punctual work-for-hire. But I promise to look a bit more into it and I will update the product description (and add an appropriate post) if I find a way to make it work world-wide.
It's a complicated issue because I reside in the European Union and, although we have a common intellectual property legislation, there are important differences between member states. Other countries are completely different animals to tackle. Although I'd being told it has being streamlined in the last years I probably should consult a lawyer foremost no matter what.
TL;DR: Not now. Probably later. I will totally look into it.