Why not just not use them?

Because whenever we use the tub, we never bother with the jets, so we would like to get rid of them, especially given the issues with mold growing in them.

Removing them, or sealing them over somehow, would be preferable to pulling out the tub and putting in a new one.

Pump 'em full of silicone.

I was thinking the same thing as trebuchet.

We will see the reverse thread in 5 years. "Moved into new house. Jetted tub filled with silicone, WTH?!"

might want to google air jet caps. Link is below for some.

Here is a link that might be useful: air jet caps

Just replace the tub. A standard sized soaking tub can easily be had for under $500. And it won't have the hackery drawback when it comes to resale.

"We will see the reverse thread in 5 years. "Moved into new house. Jetted tub filled with silicone, WTH?!"

:)