You generally write the configurations the same way: 1σ, 1σ*, etc. Being heteronuclear does not change much as far as the way we label MOs. The proportions of AO character that contribute to the MOs will be different, which can make it a little more difficult to draw MO diagrams - because it can be more challenging to decide which AOs have the largest contribution to the MOs. But MO labels are determined by symmetry, not necessarily which AOs feed into them.