refgiid foreign type is a useful converted type for iid arguments to foreign functions. When given a symbol, it looks up the GUID as if by calling
com-interface-refguid. Otherwise the value should be a foreign pointer to a GUID structure, which is passed directly without conversion.
(print-iid (com-interface-refguid 'i-unknown))
LispWorks COM/Automation User Guide and Reference Manual - 14 Feb 2015