I am assuming you are dimensioning it in a layout. Make your vport with the sphere current. Enter "solprof" at the command line, and choose your sphere. For the 3 prompts, enter yes, no, then yes (enter, n, enter). Turn the layer with the sphere off, and leave the layer with the solprof'ed circle on.
While still in that vport, choose "change space/model space" (chspace) from the Express Tools. Pick the circle just created, and hit enter.
Instead of the steps just mentioned, you could draw a circle on your layout. Since you can't use your osnaps to find the radius (quadrant, or perpendicular), you will have to enter the scale of the circle at the command line.
Either one will work for you, but with the first you get to practice on a command that is sometimes overlooked.
Flores