Hi Martijn,
that is an interesting question.
It should be possible, but that is maybe not so simple.
Set up the calculation in the normal way. Make a backup with 'cpc back'
Remove everything but not the coord. Edit the coord and change one element to a different element. E.g. Ir -> Os.
Run define again. In "ATOMIC ATTRIBUTE DEFINITION MENU" set the nuclear charge of the modified element to the values to the original. E.g. c "os" 77
Then the EHT should give something unsysmmetrical.
Copy back/coord to coord, back/basis to basis, back/auxbasis to auxbasis, and back/control to control.
Then you should be able to run it.
Cheers,
Arnim