Can you offer him a catnip toy in exchange - the way you distract a 2 year old from something they shouldn't do?

Or use the water squirt bottle to make him stop?

"Pica" is the term for eating things they shouldn't, and it usually suggests something missing from their diet; but not always.

Have you tried sprinkling some Barley Cat on his food? It is a green powder, food supplement / treat, which adds greens to their diet. Like nibbling on grass.

I can't think of anything else to try!

Sparkle eats rubber bands, I find them in her poops! But mostly I keep them out of her reach.