In theory yes, in practise, you would have to mod the case so much, it would be cheaper to buy a case that takes ATX in the first place.
First of, it will extend far beyond the available stand off mounts, so new holes would have to be precisely marked, drilled and tapped; and even this, the section that extending into the psu bay would be left unsupported.
Second, how are you going to get the psu cables to reach??
Third, how are you going to feed through the SATA leads? The atx board will block the cable feed holes.
Forth, you would be not able to use any of the extra PCIE slots, because there would be no way to secure them.
Fifth, it isnt even a nice case!!!![/quotems]
Wait, the 3 screw holes on the top of a ATX motherboard and 3 more in the middle of the motherboard are the same as the mATX screw layout for the top 3 and middle 3 right?