When you say you still want to use the ATX connectors, do you mean the molex connectors for hard disks, CDs etc, or the actual ATX motherboard connector?
If the former, then you can easily build a cable to do this. I have posted a schematic
here.
If you mean the latter, then you could use the same schematic but you would have to connect the power to the correct wires without removing the ATX connector.
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moto