What you want is Hiawatha to treat files without an extension as a CGI which can be run directly, thus without a parser. Use CGIextension to define the extenion for CGIs which can be run directly and tell Hiawatha to treat files without an extension as if they had the .cgi extension.
NoExtensionAs takes an extension as a parameter. It makes Hiawatha treat extensionless files as if they had that extension.
Try the following configuration:
CGIextension = cgi
NoExtensionAs = cgi