These are Microsoft specific extensions and I wonder if it is possible to implement them in third-party drivers. They are both needed to implement pure IOCP client and server code. The Function Extension Mechanism in the SPI page is a little thin on information...
It is achieved by intercepting SIO_GET_EXTENSION_FUNCTION_POINTER inside WSPIoctl in the SP.
Example in the SDK sample netds\winsock\lsp\ifslsp