w/o cutting down, your only option may be a trapout. The tree should come down, its a hazrd now w/ a whole near base like that.
A trap out will get the workers and they might build comb in the frames but even a trap out will need a queen from some source and can, if removed early, leave bees in the tree. Even if you trap out all the bees until the remaining workers and queen die of starvation it is hightly likely the tree will see a new hive within a year or 2. Then you start over. Not a bad setup if it yields a batch of bees every few years but I would recomment educating the owner's of the tree to the consequences of leaving the tree standing. Even sealing the entrance(s) is not a guarantee that another swarm won't make a home there later once birds and other pests open the cavity back up.