I use an X1541 cable to download .d64 files onto 5.25 disks, but isn't it possible to store the files on a PC and load the files onto a C64/C128 just as if its a 1541 drive?
It sure is possible .. have a looksie at : http://www.64hdd.com/ (http://www.64hdd.com/) rather a good application :-)
The only bummer is that is is DOS based .. not sure how well it behaves with Windows XP/Vista/7
There is a Linux equivalent as well, I just can't remember the name of the toolset cbm-something I think :-)
Mark