I know that true-to-the-lore-RPers would say: impossible, you are not an Istari like Gandalf. Lore-wise you can't be a magician, so don't include your class into your RP. But I play a RK, too and once I had the same question and got the same answers. And actually... it is true: Lore-wise you really can't be a magician.
Knowing that I went another way which connects to how Turbine set-up the RK class (they are -basically- storytellers).
In the stories I have written for her as her lore I put it this way: My RK can't use magic (period) but is able to talk to people in a way they don't really recognize but which conjures images in their imagination which can be whatever she wants them to be. In one of my stories (they currently are in German only, translation is in the works) Glenwins mother (who is a RK, too) fights a dragon by talking to him and putting images of frost, snow and blizzards into his mind. The dragon believes these images are the reality and retreats. Later -while on a journey with her family- she puts the images of a thunderstorm in the minds of her children (to demonstrate her powers and explain them how she fought the dragon) and puts a tree on fire by slashing a thunderbolt into it. But she puts it in a way that the flame is not hot which makes Glenwin aware of the fact that what she sees is not real. So in my stories the RK class does exist (and now comes the disappointment for everyone who liked this take on RK's) and is very powerful but in fact they are so powerful that they use their power of words only when absolutely necessary and only in secret so normal people would not fear them.
In other words: If you see Glenwin running around in Bree... you will never notice who she really is. To you she is just an elf.
Still this take gives me a great oppurtunity to write some stories with my own characters in them. Go here for the first (of currently only two chapters in English) if you want to read