How could i insert a handle into a steel ball so that it could roll in any direction...like a rolling massage thing?

Don't even try. You would never get a drill through a sizeable steel ball. Just buy a "rolling massage thing" if that's what you need.

Difficult - something like a shroud on the end of the handle that it pops into might work, the way that ball bearings are held captive while still being free to roll.

For that range of motion, you insert the ball into a handle, not the other way around.

The moment you insert a handle into it, it will stop rolling. It needs to be in a cage.