Hi, this is a verry interesting thread, as I tried to do a similar thing, I rewired the controller of a 3.5'' USB-floppy to an old floppy-cable. The computer (win2k or w7, I'm not shure anymore) would recognize a 3.5'' floppy, and no reading or writing was possible (just a litte LED-lighting). Unfortunately I connected the controller to a real old cable, that has no connectors for 3.5'' floppys, so I couldn't try out, if an old 3.5'' floppy would run with my device.
Considering the posts above, namely, that stillcooking had negative results with a 5.25 drive connected to a more recent FDD-controller, and that the Device Side Data adapter is read-only, I guess I will give up the Idea of having a 5¼'' floppy drive on my current computer. So I will replace the 360 kB drive on my w98 machine with my only 1.2 MB drive, where it can join my old zip-drive. (I also have USB on that computer to save on a stick, but oddly enough, it's the card I bought for my Apple G3, because the card from the PC-Store wouldn't work in the PC, but fine in the Mac. Com-connections might also work to read data from old computers, even from their floppy drives. Run intersrvr.exe on the old computer and see whar happens - use "intersvr /?" to get advice.)
Thanx to all of you for your hints, and keep posting, in case you find a solution.