If you have your heart set on adding a brake, here's one of the simple Dubro ones I mentioned.
http://www.udisco.com/hobbies/inv/DUBRO.HTM Look down for part 157. These seem destined to become pretty rare, as Dubro doesn't list them in its own catalog any longer. It's cheap enough to make an impulse purchase, and if you really want to add one, why not? Part of the fun of this hobby is in trying new things.