That is an insteresting topic indeed. I find it hard sometimes to help from slipping into the topping-from-the-bottom trap. As soon as she catches it though, she puts an end to it--which is good, because it spoils the submission altogether.
As far as being creative as a sub, I do most of the toy shopping (sometimes with orders, sometimes on my own). If I bring something home, it might get used, or it might not. And of course sometimes it might be a little more painful than I imagined and for a brief moment I might even wonder to myself why I bought it! Of course, I wouldn't dare ask for something not to be used when I was the one who chose it... something else would probably take it's place for twice as long.
Another time I get to be creative is in self-bondage. I am quite often ordered to "go to ___ room and tie yourself up using ___." I am expected to be creative within the parameters and do a good job. Needless to say, I usually have to wait there a while for any signs of approval/disapproval.