Technical question re BIP85

The index number derives a child key - could this be done with a passphrase instead of an index though (ala BIP39 passphrase)?

Ie instead of Index: 1234567890

Passphrase: One23456789-Zero

Usecase would be similar in that one seed rules them all, but instead of an up to 10-digit number which could be bruteforced, I could give a child wallet to someone and protect the master seed for them but I couldn’t get to their child seed as they’d have a master password which I couldn’t bruteforce?