I think you're wrong. I know this because deep down i know i want that dust.

Can you sign a message that proves you hold the keys without having to send a transaction??

Maybe one day the mempool clears and i know a miner and he lets me send it for free?

I could sell my dust to a miner who holds it and will only ever send it if the mempool clears but when it does he can include it for free and he can send the 100 sats still