There is no way to move a running orchestration instance between BizTalk groups.
While this is not impossible, there is no code to support it. So you would have to write it all from scratch. Accessing the Messagebox database and extracting the dehydrated orchestration and copy to another MessageBox. This would only work for dehydrated orchestration, as active orchestrations are loaded in memory on one of the Biztalk Servers in the group (not even sure if you can identify which server is running it). The issues with dependencies would stop anyone from doing this.