Well, you can "cheat" in a number of ways. You could move the model up and mount emotes to the robot. This can even allow for stuff like side jets and stuff when the robot is strafing. The problems are that there are only 4 mounts that can be used at once, including the weapon (unless you model the weapon into the playertype) and that you can shoot the area under the robot where the collision box keeps it floating. If you can modify that area with something like the critical hit script, you should be good.
Edit: Aww, I liked the old rhino.