postgresql json array index

Question

I have data for customers with more than one adresses with json representation like this:

{
    "firstName" : "Max",
    "lastName" : "Mustermann",
    "addresses" : [{
            "city" : "München",
            "houseNumber" : "1",
            "postalCode" : "87654",
            "street" : "Leopoldstraße",
        }, {
            "city" : "Berlin",
            "houseNumber" : "2a",
            "postalCode" : "12345",
            "street" : "Kurfürstendamm",
        }
    ]
}

these json is stored in a column named json of datatype json in a table named customer.

I want to query like this:

SELECT * 
FROM customer cust, 
     json_array_elements(cust.json#>'{addresses}') as adr 
WHERE adr->>'city' like '%erlin' 
and adr->>'street' like '%urf%';

Query works fine ... but can't create index that postgresql 9.3.4 can use.

Any idea?