Your problem is that hunt group calls NEVER follow twinning.
Okay, this is just a theory and I haven't tested it yet:
Set up phantoms with twinned cells, enough for peak calls to group.
For each phantom build a Call Routing Announcement, delete default VM message, time out to phantom. Maybe include message saying you're in an emergency situation. This CRA breaks the tie, it's no longer a HG call.
Build a new hunt group, distributed routing, that includes the CRAs as only members.
I believe you'll now find that calls to this group will go to one of the cells, next call to next cell etc.
Problems: this is not a real HG, calls won't move to next agent if not answered. Also calls will not hold if agent is unavailable, they'll go to next CRA regardless. Possibly solve both of these with purpose built VM greetings on each phantom's mailbox.
You could have primary HG recall to emergency HG if unanswered in X seconds, to make it automatic, or have a user change routing directly to emergency group using an additional phantom, DND and sys fwd to change path.
If you try it let us know, it would be another trick to add to our trick bag.