How I did it:
CARD A: words 1-16
CARD B: words 9-24
CARD C: words 1-8 + 17-24
you can add some dummy words to get 24 words on the card and make it look like a full seed if you are paranoid

That is not a secure replacement for Shamir's secret sharing scheme. Specifically, with SSSS, having less than N pieces of the split secret provides
no information about the secret itself.
agreed, but at least it works for me without using a tool to use SSS myself.
I would off course welcome the implementation of SSS in Trezor itself.