Missing mail options for "Send as mail" action

I have a form control of type Button, with Action set to “Send as mail”.
This works fine, but I am missing option to set the email-format to either Plain text or HTML, and missing option to add a signature file for email.
Is this possible to do this via the LL-designer, or do this by the Export option on the PreviewPage?

It is not possible to set the email format or a signature file for the email in the Designer. Please try the export options:

        LL.ExportOptions.Add(LlExportOption.ExportMailSendResultAs, "text/html");
        LL.ExportOptions.Add(LlExportOption.ExportMailProvider, "XMAPI");
        LL.ExportOptions.Add(LlExportOption.ExportMailSignatureName, @"C:\temp\signature");

Please also compare: Setting Mail Parameters by Code