So what is it you are asking for? Do you want to use an Amiga as a 1541-emulator for your C64? Or do you want to use a PC as floppy emulator for your Amiga? The latter already exists:
http://hxc2001.free.fr/floppy_drive_emulator/index.html#USBFloppyemulatorDoing it without hardware is not possible. The Amiga floppy interface is not a standard serial interface. The 1541 one is.
