There have been a few tower conversion kits that so this to some extent or other, though the majority seem to expose the A1200 backplane.
GadgetMaster's custom tower conversion was rather interesting in that he chose to mount the motherboard at 90 degrees and used cables to route all the ports to the back of the case. It meant that his accelerator card extended to the back of the case and was removable via an access cover without opening the whole case.
I can't remember seeing one that maps everything to a standard atx style set of ports but it should be possible to route some of them.
