No you are right. You can't invoke gravity in an analogy trying to explain gravity.

The same effect could be replicated in a zero-gravity environment using an alternative background force (centrifugal force, vacuum suction, electromagnetism, etc.)

Wouldn't that mean that if gravity was like this analogy, that gravity would still need an external background force to work? And how would you explain the presence of that force?

Not without a bridge for the metaphor to generalize. What parameters map to the nutjar’s selective force, size, and mass?