Mouse Controlled Sphere In Front of Character

Hey everyone;

I'm trying to get a sphere to float in front of my character in a 3d space. The cursor is locked, and what I would like to do is give the sphere an area that it can move in in front of my character, with clamp limits so that it doesn't go flying off too far to the left or to the right. Basically its very similar to this issue;

http://answers.unity3d.com/questions/347117/mouse-controlled-object-moving-inside-a-circle.html

Scribe

But I want to do something similar in a 3d space, and where the sphere would always be in front of a 3d character that can move and rotate in a 3d space. The character has a lookat script that makes him look at the sphere, so the sphere moving in front of him will act as a dynamic look-at point without it being locked to the center of the screen.

Any ideas or help would be appreciated.

-Jon