@mvertens my understanding is that you are doing this along with https://github.com/ESCOMP/CMEPS/issues/131, but let me know if you're hoping for some help from me on this.
This is at least partially done in cism2_1_73. There may be other changes needed, but the changes from @mvertens in that tag put us well on our way towards addressing this need.
Connected with https://github.com/ESCOMP/CMEPS/issues/131, I think there will need to be some changes in CISM's nuopc cap to allow multiple ice sheets.
@mvertens my understanding is that you are doing this along with https://github.com/ESCOMP/CMEPS/issues/131, but let me know if you're hoping for some help from me on this.