How to ground private 2/0 aerial triplex from meter to garage
Sadly, with this type of feeder, you are obliged to use the bare wire as a safety ground (unless you can get a waiver from your local authority to treat it as a service).  

That gives you two options: run 120V-only, or run 240V-only and use a transformer to derive 120/240V service.   This might be sensible if the lion's share of your load is 240V only and your 120V loads comprise only receptacles abd lights.