I think I finally have it working. Here's what I did:
Built a rotary HG (broadcast won't work)
Put an unused analog station as the only member
Assigned the analog station as an Answer DN on my HG sets
Overflow the HG back to itself.
Now when I call the HG DN, the first call rings on the Answer DN button on all sets. A second call to the HG rings on the intercom key on all sets with the ADN assigned. Third and subsequent calls to the HG continue to ring on other intercom keys, allowing the operator to place the call on hold and answer a new call. Since the calls appear to the set as Answer DN calls, they don't follow the forwarding for the set, and total calls for the hunt group will equal the total of all the intercom keys on the sets where the Answer DN appears plus the number of sets that DN appears on.