Well, how about the Ctrl + J button when used, does something more than just an animation? I mean, it could act as a kick to the player standing next to the horse, which would give sense to the whole control or action.
Also, being able to whistle and call your horse would be nice. Or jumping on top of it and an having animation similar to that of the Zorro when jumping from a roof onto horse. [Imagine how cool It'd be to be swarmed by a crapload of enemies, then in a swift movement whistling to your horse and jumping on it evading your enemies; simply awesome.]