Hi @hot_geek,
I guess it could be another way to solve your problem.
Out of the box you won't be able to change the scope (you'll need some code or even database change... and I'm not sure about the consequences).
Categories aren't just an attribute for porducts, a Category is an entity itself so you can't handle in the same way that any other attribute.
What you're trying to apply, I guess, is to add a product to one category in website A and the same product to another category on website B.
Normally you should be able to add the product to both categories and then enable or disable the category.
