Heh, i did something similar. My group was in a crypt filled with ghast and ghoulies, so i altered self into an ogre. Needless to say that my grapple was sufficient to grab and throw a baddie quite a distance. My DM ruled depending on the attack roll ... d6 for every 5-10 ft thrown. And since it was a low ceiling ... that added another d6 for hitting that first befre hitting the mob. Mob took half dmg.
After this we called it OGRE POWER oh oh huh (Tim Allen impersonation)
After this we called it OGRE POWER oh oh huh (Tim Allen impersonation)