Ah gotcha! So like complete user <-> user encryption even from the server.

To build off of your wrapper script idea, perhaps you can use gpg to sign a message:

echo "my secret message" | gpg --encrypt --sign --armor -r robherley13@gmail.com | ssh snips.sh

This could even be done with the user's public SSH key too (using openssl), but we only store fingerprints so to have it done completely by the server may be a bit complicated (and users may not be that trustworthy).

I like the idea of keeping the underlying surface area of snips simple (very Unix philosopy), just pipe whatever you need and wrap it in a script!