I know that Amstrad and Sinclair Spectrum +3 can use quickdisks so can they be used to copy FDS disks?
Maybe if you could code some very hardcore assembly language program to duplicate raw sectors it would be possible, but even then it's possible that the head alignment would not be the same and you wouldn't be able to read anything. And I've read before that FDS disks are not like a normal disk, but like a 'stream' of data recorded on them. More input from FDS experts would be appreciated ;).
the disks are shaped a bit different, you would have to do some hardcore modding
Ummm, no. You asked the same question on Tototek. That thread goes over 99 percent of the FDS copy methods.