What specific challenges arise when using rundll32 with RegisterXLL() to load a remotely downloaded DLL, and how are they overcome?

Under rundll32, `WScript.CreateObject` is unsupported and must be replaced with `new ActiveXObject`. Also, saving binary files via `Scripting.FileSystemObject` fails, so a workaround encodes the DLL as base64, saves it as text, and later decodes it. To avoid pop-ups, `document.write();` is added. These adjustments are detailed in the article's extended usage section to ensure silent execution.