I have.
Thing you need is the backplate of a dead ATX psu and then use that as template for the holes you need to drill.
And if you use spacers between the case and psu, you should be good.
Or if your good with a dremel, you can make it fit, the problem is the AC line in connector sticks out by about 2mm's.
My A2000 power supply is dying, I plan on getting the ATX to A2000 MB cable adapter. and a Seasonic PSU. Has any one else put an ATX PSU in their A2000?