This soft fork orphans any new csam-containing block that gets mined by having miners hash on the previous "clean" block. This effectively bypasses the csam block by creating a longer chain of clean blocks and leaving the csam block (as well as the miners revenue) orphaned and forever discarded by node consensus. This will signal to miners that allowing csam-containing transactions in their mempool will corrupt their changes of having other miners on the network accept and mine on their block.