OP_DROP might not work as the BIP16 spec specifies.
"Validation fails if there are any operations other than "push data" operations in the scriptSig."
Good catch. That is weirdly worded and I have no idea what it means. As written no no multisig P2SH script would be valid. is not a "push data" operation. I will try testing the OP_DROP script on testnet.