Bit late to this party, but:
In theory, kind of. The mainboards from those AIO Performas are actually identical to ones used in desktop models - like the 6200-6300 series you mention in the ATX power supply conversion link.
Now I don't know about specifically into a mITX sized case, but you could most likely get it into something more conveniently sized for you. The main drag is going to be getting the wiring harness out of the original machine, and reconnecting that to whatever you want to use.
These two series (the desktops and the AIOs) use a long